I think this is a good assessment, though I think DL is a lot less likely than you do. If it was 2015 I'd say DL was about as likely as you say, but the idea that they're going to do a white people-centric (with all non-white cultures as "barbarians" no less!) setting in 2021 (part inspired by a religion which has its struggles with race, even!) after all their public commitments and work on diversity seems... unlikely. As I've noted before, Taladas might work, it's a vastly more diverse setting, but Dragonlance it ain't.
I think this could all be remedied. First of all, aren't Ergothians non-white? It has been awhile, but I don't remember as "barbarians." Other than Theros Ironfeld, they didn't feature much in the Chronicles but could be more prominent in a 5E treatment. The Que-Shu could use some work, but not as much to make them less "barbaric" but to change the whole "savages seeing the light of true religion" thing. They could be tweaked to be a vital, indigenous people that never embraced the pantheon of gods but have their own valid shamanic beliefs. This, of course, would change the substance of DL a bit in that the "true gods" thing would have to be altered a bit, or more ambivalent.
If WotC went full in and did a couple books (say, setting and adventure, with rules in both), there's no reason why a setting book couldn't include Taladas and Irda and Minotaurs as PC races.
I think as someone else said, the selling point of DL would/could be dragon-riding. A dragon-centric campaign would probably be quite possible, especially with rules for aerial combat.
I don't think gully dwarves are much of a problem because they really only had a place in the novels - no one was playing gully dwarf PCs, afaict. An RPG treatment would barely have to mention them, if at all. They could also be adapted a bit, with some kind of origin that disentangles them from certain associations. Meaning, maybe they are the descendants of dwarves that were cut off from civilization for millenia and devolved.
Kender...the problem is mostly/entirely table dynamics. A paragraph or two of player guidance should suffice: "Your curiosity leads you to acquire things, although you tend to be a faithful companion and rarely take from friends and, on the rare occasion that you do, give it back." Or some such.
Meaning, I don't see any of the "problems" as insurmountable - they could all be adjusted as necessary without changing the essential qualities of what makes Dragonlance distinct, or angering any but the most fervent traditionalists. Whether or not WotC does this is another matter.
Point of order: there already is a 5e Forgotten Realms setting book*. It may be not very good and limited in scope, but so far as WotC are concerned they have done that, and wouldn't count it as a "classic setting" - a current setting is not a "classic" setting, just as a 2016 Ford Focus is not a classic car.
*Two actually, Acquisitions Inc is technically a Forgotten Realms setting book.
Yeah, but...semantics. I interpret "classic settings" to be anything published before WotC's tenure - so everything except Eberron, Magic, and Exandria. If they said
legacy, I'd agree with your take.
I really don't see the down-side of a full-blown FR setting book. Most importantly (for WotC) it would probably sell quite well, given that it is the default setting for most of the adventures. I can't speak for the young 'uns, but I imagine they want to know more about the world they've been playing in.