I'm happy to hear you liked the core-loop as is. I'd be interested in keeping it the same, but there should be some more content or meta progression so people don't get bored even if they are not progressing. I'll think about how we could resolve this issue. If you have any suggestions, please don't hold it back (unless you want to create a similar game).
GameMaker is an interesting suggestion, I haven't thought about using other engine than Unity as I have several packages/assets already and I'm used to the ecosystem. Anyways I'll look into that engine as well, a bit of an environment change wouldn't hurt!