It is social media, why does this need to be handled at the protocol level? Post a final message on the "You@ServerA" account saying "This is my last post here, keep talking to me with my new account: You@ServerB"
Anyone who visits your old account will see the last message. Anyone who sees that message and can't muster the effort to make 2 mouse clicks probably isn't a follower except from a numbers perspective.
If you're content losing 90% of your followers because the server you host on decides to implement draconian censorship or start charging $50/mo, then yeah, be my guest and use the protocol as it is.
I personally think tying identity to a particular server instance is the wrong approach, whether you can beg your followers to come find your new location or not.
Also, your method only works if the server is still up. If your host server is taken down indefinitely, then you truly do get to rebuild your network again. Fun.
As a human, social, user of Mastodon, yes that's totally fine with me. 50k followers is absurd, I have maybe in the 100's of social connections, and realistically only maintain in the dozens of meaningful conversations with people. I just want a means to have those connections that's not feeding some omnipotent beast.
I'm assuming your values are something else. Do you monetize your social media followers/follower count in some way? For some professions it's smart and necessary, but for my career it's not relevant in any way at this point.
I'm thinking of business use-cases, yes. For instance, I agree with you, if my personal twitter was lost, I wouldn't lost any sleep over it. But if my business twitter was lost, which has almost 1500 followers and took years to build up, I'd be pretty upset. And I don't have a deep connection with all of those followers, but if 10% of them see each post I make, that's a lot of marketing value to me.
Anyone who visits your old account will see the last message. Anyone who sees that message and can't muster the effort to make 2 mouse clicks probably isn't a follower except from a numbers perspective.