Meh, just run several associated services and keep the same username on all of them. Nothing is interoperable, stop trying to force it. And a rogue app with bad user data handling practices is still going to leak your data, even if you store your copy of the data securely.
My fediverse accounts are always “patrick@<service>.bestiver.se”. I currently am only running Mastodon/Lemmy and a few supporting services (e.g. a link manager - https://bestiver.se/@patrick), but I’m adding more as I get to them. Pixelfed, Peertube, Loops(?), Piefed…
Adopting this ActivityPods thing looks like it will require each Fediverse project to make what I’d guess are fairly significant changes to their user data handling, and none of those projects are properly funded for this. In fact what this actually seems to be doing is asking every other Fedi app to build on top of their user data API.
I applaud the attempt at building a new standard in the Fediverse, but I doubt it’s going to happen.
On the feature side, according to Mastodons recent 4.3 release post development is only 4 full time employees and a budget of under $500k annually. That is basically nothing in the realm of social media companies.
Improving Mastodons features requires money and resources, but Mastodons users are unwilling to pay for instances and unwillingly to fund development. Hell, the .world folks host a bunch of instances for collectively hundreds of thousands of users and they take in about $1k a month in donations. I’m surprised that even covers hosting costs.
So…it’s no wonder that it isn’t going to be as polished as other social media in ways that would reduce the attrition.