Exactly. There’s no reason you couldn’t create a mastodon/kbin/lemmy/+ app which lets you log in and switch personalities on the fly, either aggregating all feeds into one or showing you individual feeds (like the Gmail All Inboxes). You could even have custom aggregation, like having it show you all of the c/+m/ [!foo@*.ext] threads in one combined feed so that you can see everything related to foo in one place no matter what instance its hosted on.

All it takes is someone who wants to create it and the programming to make it and maintain it. Which is kind of like saying all I need is a desire to retire and five million dollars; no matter how unlikely to happen, it’s still a true statement.