If I was logged into several instances at once in the client and seeing the composite feed and then could choose instance when replying or posting (with some set default, like from: field in e-mail clients) lemmy.world could ban piracy all it wants and it’d still be in my feed without me having to leave it or change instances.
There should be an option to see all posts on our feed from all our instances. Then when commenting choose the instance from which the comment has to be posted.
This needs to be done carefully. At the extreme you’re asking every instance for a list of posts from all instances. It could become something like a DOS. Having just a few accounts should be fine though. Or just asking one instance for “all” and others for “local”.
Maybe a digital signature of some kind to copy and paste from one account to another, or account to account import/export of the subscribe list.