I think there's an important caveat that should be applied to that slideshow, which is that it appears to assume that visual distinctiveness — particular kinds of visual distinctiveness, even — is just about the only consideration that needs to be made when designing a character, even at a basic level.
The slideshow specifically cautions against designing a white character with no markings, and I find that a little strange. In the first place, the slideshow uses Baymax from Big Hero 6 as its example of a white character, who is as white with no markings as any character could possibly be. And in the second, one of the most popular furry fanart subjects of the past year has been Toriel from Undertale, equally white with no markings, but certainly visually distinct from Baymax and from other characters.
One thing that makes Toriel and Baymax unique is their body type, which is a consideration glaringly missing from the slideshow in any detail. Sure, lots of time is devoted to particular facial features, hybridization, and the like, but there is no analysis of their silhouette. One thing that's been particularly striking for me being Drakitten's sober second thought on her commissions is that I got to see lots of different body types represented in her characters: Muscular and lean, thin and fit, curvaceous, fat and pudgy. I'd be able to pick all of them out of a lineup just by silhouette, because they're so distinctive. It seems to me to be a symptom of some of the bad habits picked up from more mainstream media that it's considered a virtue for all our characters to have body types within a narrow range — within the same gender, of course, as it's also seen as a virtue that we should be able to gender a character in an instant to decide whether it's okay for us to find that character attractive. Look at all the characters depicted in the slideshow, and really think about how uniform their body types are compared to the body types in the four links above.
But even if you decide you want to have a character who has stereotypically idealized forms of beauty (through a furry lens, anyway), you can still have a unique silhouette. Even though there isn't a great deal of body-type variance in these characters, they're still instantly identifiable from each other, and I think for a lot of them, that's true even though they're in the same position: The otter character (bad palette), the lemur-ish character (good palette), the shark character (bad palette), and the otterdragon (species hybridization) all have the same position, but you'd never confuse them for each other. Traits help, but specifically thinking about the silhouette of the character allows you to control the process. Do you want larger or smaller wings to change the space a character takes up? longer or shorter horns? A stubbier or more tapered tail with longer or shorter spines or ridges? What does this do to the space the character takes up?
It's also significant that we have an emotional connection to Toriel, and as a result, we don't need markings or other features to think of her as interesting; we have her personality in her actions and in her words, and we carry that over to the art we see of her. This seems to be a missing element of the character design process, a kind of 'method designing': not only using allegorical physical details to draw out the personality of a character but actually giving them motivations, hopes, dreams, even flaws that inform their mannerisms and allow us to project those traits onto them. Toriel looks motherly, to be sure, not only in her traits but in how she carries herself; but she also acts motherly, protective, stubborn, and we know this every time we look at her, reinforcing what the visuals imply.
These traits can be associated with the character's species, or they can be disassociated. I have three bunny characters: Glire, Carmen, and Igneus. Glire is a feminine character, an avid rollerblader who does a lot of heavy lifting, and a sweetheart who just wants to please others. Carmen is a character heavily damaged by her upbringing and whose main motivation is transforming the circumstances of her past into something beautiful, while at the same time dismantling the system that produced her situation. And Igneus was intended specifically to be a subversion of the tropes of bunnies: co's a violent, iconoclastic firebrand with a strong moral core hidden under a chaotic personality and a vendetta against a world that abandoned co. It can be just as rewarding to deliberately subvert and question the merits of the stereotypes associated with those species as it is to draw from those stereotypes.
The slideshow in general seems to have a professional perspective of character design, which I feel only tells half the story. Especially in the furry fandom, people make characters to represent theirselves, and download their personalities (or a personality they'd like to project) into those characters. I think that's an important fact to address: it means that those characters have an emotional context that may not be visible to those who don't know them, and to judge a character wholly visually is, to some extent, to judge its creator on those merits. Once you do know them and understand them, however, then you have the context to appreciate them. We know that we perceive other people's appearances differently when we know more about that person; there are countless stories of people who find their partners more beautiful the more they fall in love with them, or even the opposite, finding them unattractive as soon as the relationship falls apart. If we can get to know these characters, it matters less whether they have interesting markings or striking colour palettes, because we'll be able to 'see' what we find interesting about them.
All this seems rather high-level for what bills itself as a basic talk, I know. But the simplification of these discussions down into a form beginners can use as a guide is our job as the people who know what we're talking about — It's our responsibility not to give people a bunch of advice that might be useful in the short term, as it narrows the design space, but that also a) upholds stereotypes about what characters should look like and b) those beginners will have to dismantle when they start to outgrow that advice. And really, it's not that hard to simplify this: Does this character act like we might expect when we hear 'cat' or 'dragon' or are they completely different than their species might suggest? How does this translate to their mannerisms? What kind of body do we want to design for them, and how does this decision interact with the 'ideal', stereotypical body type and with gender and species expectations of their appearance? How do they take up space, and how do we want them to take up space? What can we say about who they are as a person so our audience views them in a different light, or to emphasize the physical traits and mannerisms we've given them?
I really wish this slideshow spent some time interrogating the market and its preferences, even only in passing. I admit that the audience for furry art focuses on whether a character has a model body, or conventionally attractive or unique features; I also admit that these things are shallow, structurally prejudiced ways to judge a character, and it's not assumed that following the path of least resistance is the right way to go. This fact is core to the discussion about designing a character, even at a basic level: If you want to make a character people will like, you are either going to have to break the mold in a compelling way, find an underserved niche, or give the generalized "audience" what it wants — and, on a collective level, that "audience" is prejudiced and entitled in specific ways you will have to decide whether to pander to.
Especially since this talk seems to be geared towards artists making money off their art, we shouldn't shy away from discussing what we may be required to do with our skill in order to make that money — or where we draw the line. Most artists have things they won't draw, usually specific kinks. They specifically limit groups from being potential sources of income, due to their own personal comfort levels. Are we comfortable also to constrain ourselves to the safest choices within the most stereotypical preferences of our audience?
There's no right answer, I don't think. There's only preference and, to some extent, financial necessity, depending on the situation. But we owe it to ourselves to ask the question.