One of the main justifications as to why the AI doesn't simply get out its flamethrower and burn you inside your foxhole is that in the beginning, you're extremely weak and the AI is busy dealing with other matters. It doesn't feel the need to spend that many resources or effort to deal with you because you're not a threat and it has bigger fish to fry.
What if those bigger fish were inside the current galaxy? As in, the other force has a tangible presence and territory in the galaxy and is actively fighting the AI for control? For instance, they could still fighting against some zenith remnants, or a spire colony, a neinzul hivemind, etc.
I think it'd be pretty cool if forcing the AI to redirect its resources to dealing with us would actually have a significant impact on the health of the AI empire. If we force the AI to send a mothership after us, that's one less mothership they can use to deal with spire dreadnoughts. If we end up amassing enough resources to hassle the AI and spook it, it should really make the AI hurt, instead of the AI completely rising to the challenge regardless of what you do.