That sounds logical. Federation without conditions would make no sense at all for Meta. You could then run an ad-free Threads copy, create any client you want, easily train your AI on their content.
Surely if such deals materialize, many idealistic Mastodon instances will defederate with Meta. A few big Mastodon instances might not. Next, the idealistic Mastodon instances will defederate with the Meta-compatible Mastodon instances.
Which...makes large Mastodon instances pretty pointless. They'll be largely isolated from the rest of the Mastodon part of the fediverse. They can interact with Threads users, but in that case...why wouldn't users simply use Threads?
Also that it they will only peer with hosts that sign an agreement with them. There is rumour of $$ involved.
I think you can guess how this will all shake out.
(Snarky aside: maybe Truth Social will federate with them?)