Bloat doesn't have a firm definition. I think it's at the intersection of being unable to find content you want easily (by being uncertain of the location), being unable to easily transport the material, having books that might never be used in play, and the balance of material being affected by power creep.
Yeah. I was really annoyed the first time I found a 4e feat in one of the books that was unconditionally better than a parallel feat in the PHB.
I'd love PDFs as well.
Digital content is neat, but it does compete with the physical books, which is unfortunate. It gets necessary for games like Pathfinder or 4e, but I don't think it's as needed for 5e. There's just less math and complexity in gaining levels.
It's true that it competes somewhat with the physical books, but it's notable that everyone but Wizards seems to think it's a good deal for them. And while it may not be as-needed, I would absolutely love to have searchable text for the 5E rules, instead of physical books. Well, given me, probably in addition to physical books. But searchable text is such a huge advantage. So is the ability to have the complete text of all three core books in an object that weighs less than half what one of them does.
Other than that, I'd like 2-3 more subclasses for most of the classes. Maybe 3-4 for the barbarian, bard, and druid who are a little under loved. But that's far less content than you could squeeze into a single 256-page book, let alone a full-sized PHB2.
Yeah. If they did that, plus maybe some psionic classes and some other stuff, they might have about enough for one reasonably solid expansion book.
Seriously, look at the numbers. Each subclass takes roughly 3/4 of a page, so if there were 4 new subclasses for each class, that'd be around 40 pages. Maybe 50 with art. To almost double the subclasses in the game. Add subraces for each race and you might get 60 or 70 pages. What do you fill the remaining 180-odd pages with? Some spells, some feats, some martial manuevers. Yeah, that'll kill 20 or 30 pages. 150 more to go.
What then? Double the content? Triple? At that point things just become silly...
At that point, the game is pretty much done. WotC could release a single giant splatbook and "finish" the edition in terms of support in a single month. There'd be room for a big all-in-one tonal expansion (like psionics) with classes, subclasses, races, monsters and the like, but not much else would be needed.
Or they could space out that content over three or four years, with small releases that are heavy in flavour (like in the post-Essentials 4e line). Making each book with its content more anticipated and exciting.
They could, but that would most likely result in a lot more paper to carry around to get the same game mechanics, and that doesn't entirely appeal to me.