If things played out in just the right way, this could push them away from the Fediverse entirely, I'd think. Seems it would be hard to monetize any traffic coming from the Fediverse end of things, which would make the whole thing more of a headache than it's worth for them.

An instance that was explicitly set up as a read-only backdoor to Threads probably wouldn't stay federated long, but is a cool idea at least.