Hi @KStoller-WMF! Since you mentioned yesterday that this was a potential project for the coming year, I wanted to stop by and offer some early thoughts.
Overall, this project would touch on a lot of cultural aspects, which introduces some uncertainty as wikiculture can always change. One path I could easily see this taking, though, is that if a structured user profile is offered to newcomers, it'll quickly become associated with them, and no matter how good its features, users will want to stop using it as soon as they become experienced enough to learn its reputation.
Newcomers are often very eager to create user profiles, so I don't think you'd have any issue with uptake. But before we get too excited about that, uptake alone wouldn't be enough. The community has made very clear that userpages are not just a blank canvas, but rather required to aid in the development of the encyclopedia. If an easier way to make userpages resulted in newcomers doing so, but then never going on to make edits to articles, that doesn't help us.
Worse, the ability to create a userpage is currently an incentive for newcomers to learn basic wikitext. If an easier way to create a profile was introduced, this incentive would be removed.
Given all that, I'm not sure this is something to prioritize, given that it's high-effort for uncertain benefit and has drawbacks. I'll note that, while an editor proposed it for the 2022 wishlist, it didn't do all that well — in the bottom half in terms of number of votes, and several opposes despite those being uncommon for wishlist items. For lower-effort alternatives, I think the community could perhaps improve the editnotice for blank userpages to help alleviate the "what do I do with this space?" question; your input would be welcome on that, but there would not be any technical elements that'd require developer support.
Cheers,