I posted this over on Discord this morning in response to the same question:
We are way too deep into VaM2 to switch engines now. A change to UE would cost years in development time. This move by Unity is ridiculous and they are facing huge backlash already. If they keep moving forward they are going to face a lot of legal battles, and I would join in on that if necessary. I'm hugely disappointed in Unity and this is killing whatever positivity the Unity brand had left. If I was starting over, I would not choose Unity for the project. I think Unity is going to have to rollback on this proposed change to save face. I don't think it will ultimately affect VaM or VaM2 because I can't see how they can possibly roll this out in the face of such negativity, and I also don't see how they can technically pull off accurate install and revenue numbers without companies self reporting.
VaM2 moves forward on Unity. The VaM2 addon kit is Unity based and highly tied to that. I'm not throwing away years of work to start over on another engine.