Defederation is never going to go away because there are whole instances out there dedicated to hosting illegal material and because, lets not forget, Admin's want the Lemmyverse to succeed and a way for it to not succeed is to federate with instances that do this and also have userbases made up of racists, homophobes, transphobes etc. Literally no one wants to be constantly firefighting their own individual user block lists to keep blocking hundreds of awful people. What they want is to spend time on their communities. That's why instances have codes of conduct stating what they won't allow. It allows quick, painless instant separation from arseholes without putting the onus on all their users to individually block users from whole instances.

But, as Admin and Mod level tools (and to a lesser extent user tools) get developed, defederation will happen less and less.