I doubt it. I admin a lemmy instance and a regular fediverse instance, and I use them both very differently, because their interfaces lend themselves to different uses. Even though they can communicate with each other, trying to navigate a large number of lemmy groups from Hajkey would be annoying, and trying to follow specific users from lemmy would be annoying.
An all in one app would mash that all together, which would probably be overwhelming and confusing
But the cool thing about open standards is that there's a clear pathway to creating an everything app. Especially if decentralized ids gain some traction, then we could have an app that combines mastodon and pixelfed but presents the different posts in a sensible way.
I can't really wrap my head around what such an app could look like, but it's much more feasible to build one than it would be with closed services. I'm hopeful that freedom to experiment without lockin will lead to some really neat ideas