Very happy to hear You like the game!
Yep I have some next rules in mind, for example that every column has to sum up to a given number.
But as You said, coding them is a little bit harsh.
As far as I know there is no way to just code every one rule by itself (which is a little mathematical puzzle on its own) and then combine them. I have to make a case for every combination of rules there is which is not that bad for now, but could quickly get out of hand when I add more. Fortunately some of the cases are cut down by just rotating or flipping the board.
As I'm working on improving the game now, I mainly focused on adding new items to the shop and actually fixing it hah