I think without account karma the loyalty to the account would be less for the average person. The more annoying part is the communities you've subscribed to and finding them again. I think a simple download of a list that automates resubscribing on a new account would ease that issue for most people.
For an active user would be that you lose access to communities you created. That is a real logistical problem. I started on lemmy.ml and crelated a community then realized that lemmy.world ran a lot smoother (at the time) and moved. I luckily still have access to my original account so I was able to appoint my new account as a mod. So problem solved. If your instance splodes you lose that ability. But likely your sub went with it too anyway.
I guess the real problem I am identifying here is while the fediverse itself is decentralized, your account isn't. It is locked onto one instance and the fediverse is volatile.
Maybe add an ability to attach your account on 2 or 3 instances and keep them synced? If one goes rogue then you have a backup that's still on the fediverse? You can then defederate yourself from one if needed.
Idk.
I guess running a small private instance just for yourself is the best answer.