AGPL was already used by most existing Fediverse platforms, and ensures that all code changes need to be published. Its basically an improvement over GPL which also takes effect when the software is hosted on a server, not running on the user’s computer.
The Anti-Capitalist Software License is not an open source software license.
It would be relatively easy to write a script/bot which fetches the list of communities from a given instance, and then subscribes to all of them from another instance. In fact I heard something like this already exists, but dont know the name.
I think its totally normal that instance sizes follow a power law distribution. Its similar to many other things, for example there are few large cities, some medium cities and lots of small cities. The wiki article lists many other examples. So I think its fine as long as there are no intentional attempts to lock in users into large instances or limit federation.
You can already interact with Peertube videos and follow their channels. Thats possible because Peertube also federates groups (communities). With Mastodon thats not possible because it doesnt have groups, and Lemmy doesnt support content outside of communities. At least not without a full rewrite, which doesnt make sense considering that KBin and dozens of different microblogging platforms already exist.
Lemmy was meant to be a Reddit replacement from the beginning, so it was always supposed to take off. Even in the early days the tech was working quite smoothly and users were happy so there was no real doubt about it. The only thing missing were more users. However I had no idea how a real migration would actually look like, so it was really overwhelming when last year people started to flood in and everything got overloaded and broke down.
More importantly it would make exports extremely large and would cause a lot of server load to import/export. Plus you would end up with duplicate posts and comments which seems like a bad idea.
In the future it could make sense to make a protocol extension to send multiple activities in a single HTTP connection. But for now its probably not worth the effort, considering that it would break compatibility with other Fediverse platforms.