I mean, spells like Wish are going to be basically impossible outside of going the AI route (which is an entire can of worms).
Wish can duplicate any other spell, or it can have your own effect (with a chance of it being monkey-pawed plus you never being able to cast Wish ever again).
Also bear in mind that it's not "just" rules for moving numbers. You have to have particles, animations, etc. You can't just have conversations, you have to also have SFX from impacts, camera shake, UI elements, etc. When you start to get into the world of "anything is possible" you kind of have to go back to basics, text-based adventures.
With AI stuff, maybe some of that can be done - but AI is just so incredibly slow in its current form. It won't stay that way forever, mind - I think the best comparison is graphics in the 1990s. Graphics were incredibly basic because anything complex would take ages to render and couldn't be used in games. Over the next decade, things were built to specifically speed up that process, and now modern GPUs can easily keep up with the highest-quality CGI without much fuss (there's a reason why Disney has the Volume, which is essentially just running CGI in the Unreal Engine alongside the actors in real-time).
But until that, we're going to be pretty limited. It's going to be impossible for any kind of free-form rules to be implemented, unless options were restricted to such a point that it's basically a completely different spell.