I mean by this, is there any website that with one sign up would allow you to have a matrix account, lemmy account, mastodon account, etc. If it couldn't be done with just one url it could be made a thing where it would be service.website.tld (so an example would be lemmy.myreallycool.website). Is there anything that already exists like this? I think it would be really cool to just have one home server for everything that you need, and to also have the same identity on all platforms. Another actual practical application of this I can think of is if you want to message someone you know from lemmy but on matrix you could just change the domain (ex: @username@lemmy.myreallycool.website to @username@matrix.myreallycool.website) or something like that. I know that one of the big appeals of the fediverse is that the accounts are interoperable but I still end up using a different account for my mastodon and lemmy accounts for example. I'm genuinely interested in something like this as I think this would be a really cool idea.
Then, would it be a better idea to create one mega-fediverse app that combines but also separates all the different features of each platform (eg: when viewing it on a browser, it would have a Lemmy tab, matrix tab, mastodon tab, etc) and then have the functionality and format be separate for each one of those instead of trying to pull a "can do everything, good at nothing" type of platform? That would solve the email issue, but I feel it would be more complicated to implement but I've also never developed anything remotely like that ever and so I'm not qualified to speak on it.