Federation is a people-problem, not so much the resource problem.

Mastodon servers defederate because the people (or rather, the admins, perhaps prompted by the users) of instance A don't want anything to do with the people (who toot at the discretion and policies of the admins) of instance B.

Codeberg's AI position, as stated and voted upon, does not mention resource usage at all. That's completely invisible from the discussion. It is exclusively argued against on accord of 1) unclear copyright ownership, and 2) users have no idea what's in the code, therefore it could be full of security flaws or harmful code.

https://codeberg.org/Codeberg/org/pulls/1253

So they would not want to federate with another instance that used a lot of AI-generated code, even if it claimed an open license, even if that federation caused little-to-no usage of their CI. They would fundamentally disagree with any other instance that allowed mostly-AI-generated projects. They would therefore block such instances, if federation was a thing.