still I wonder whether the lemmy system of federating all upvotes would scale well if the number of users grows to that of mastodon and beyond ?
It’s a good question and really we just don’t know yet I think. It’s very hard to predict performance of complex systems. The only way to know, is basically by measuring, and the only way to do that is if we actually had that amount of users.
Could there be some intermediate compromise solution (e.g. federate batches of 100 likes)?
Unfortunately ActivityPub has no way to “batch” activities like this.