@Nathaniel Lee, I think the majority of your points are good ones, and I certainly don't mean to start an argument. But I would like to dive down just a bit on this one part:
Again, not really, since the majority of players don't use homebrew classes in the first place. ...
I still don't quite buy this ... I wish there was some statistic we could consult that would settle the question, but I don't believe there is. In the end, we mostly have to agree to disagree, but there are a couple of points that seem salient.
In my very first game of D&D (this woud have been Basic rules, I believe), we homebrewed. Then I moved on to 1e, and we homebrewed. Then 2e, and then 3e, and then 3.5e, and then Pathfinder: homebrewing every time. Now we're on 5e, and we're still homebrewing. I don't think I ever even
met anyone who wasn't doing at least
some homebrewing in their games. Now, as you point out, the majority of current 5e players aren't like me (or most of us on this site, I suspect): they haven't been playing forever, and thus homebrewing forever. But a significant number of these players—perhaps even a majority—are learning about D&D from streams and podcasts. What DMs are they watching/listening to that don't do any homebrewing? Not Mercer, Colville, or McElroy(s); not Iyengar or Woll or Walters; not Phoenix, nor Mulligan, nor Hulmes, nor Vorpahl, nor Tang. Maybe they're not learning from actual play, but more from advice streams? Dungeon Coach talks about homebrewing a
lot, as does Nerdarchy, or Dael Kingsmill .... It just seems to me that, even if you're brand new, you would have been exposed to the concept of homebrewing, and you've explicitly been sold on D&D being a game where you can play whatever you like. So I'm not sure why the majority of these new players
wouldn't be homebrewing.
As far as whether not having this feature will prevent them from "winning" the market in the long run, what I can say with a lot of confidence is that Curse is going to prioritize features that users have actually indicated that they wanted since they want to, you know, make money. If everyone and their mother wanted a homebrew class feature for the platform, they would be prioritizing that. They aren't.
I hope you're right. Whether a company actually produces what their customer wants isn't a given, though. Especially at the scale DDB is now ... it's
possible (and I stress I'm not saying this is true, just that it's possible, based on my experience in the industry) that the folks at the bottom (devs, customer support, etc) are telling the higher-ups that this is what customers want, but the higher-ups aren't listening. Unless they're doing some focus group testing or that sort of thing, corporate executives can be sadly unaware of what their customers actually want.
On the other hand, I know Morrus is on this site every day, and he knows what his customers want, and he's producing homebrew material. And I know that Colville is doing surveys asking his customers what they want, and he's producing homebrew material. So
somebody must be asking for it.
You mention that you tried to create your own character builder more than once and acknowledge the difficulty that lies in such a project — imagine that's what you're trying to do with a team of 2-3 developers and no real financial backing in the hopes of getting something out the door that people would be willing to actually pay money for with the ability to scale as an open, web-based application would need to. Like you said, not even remotely easy to accomplish.
This is another excellent point that you make. I do want to clarify, though, that my lack of resources had nothing to do with being able to handle homebrew: that's a question of designing for that up front, which I have always done in every one of my attempts. My lack of resources mean that none of my results have been
scalable, which as you (and Umbran) noted, is
crucial to producing something that people can actually use. Otherwise, you're just producing toy software ... which is, sadly, all I've ever managed to produce.
So the DDB devs managed to produce something scalable which doesn't handle homebrew very well, which, from my perspective, feels like they got the hard part right and whiffed the easy bit. But I do concede that I don't have any special knowledge of their challenges, so obviously I'm just projecting my own mindset onto them.
Counterintuitively adding engineers makes a project take LONGER.
Heheh. Yes, that's the main thesis of
The Mythical Man-Month, which should be required reading for all developers.

But Brooks also tells us how to address those problems, which is the real point of the book.