Guys chill, influencing engine being renpy thing talked by many people many times in dev's discord channel, long time and several updates ago. I really don't think he'd push things further with the first game and go for a game engine change. If you can run it now i think you can run it with upcoming updates and changes as well. Even if you can't run it with a more complex AI as long as AI is optional you can run normal (No AI) version.
Influencing 2? Dunnow about that. I also talked with dev a couple of times. (Been a while, there was no influencing 2 talk) From the impression i had, i am thinking he will first want to satisfy himself by making a good and different job again.
If i have to make a guess the new engine for second game, i say Unity. Just a guess.
BUT then we don't even know if influencing 2 will actually happen or not right? Or first one will get abandoned or not (i hope not) So for now just chill.