When you have your own MPS I do not see why it is not leveraged. If it is used this would help better experimentaion and language hacking. So it would be ideal if Kotlin gradually moves into MPS implimentation.
No it wouldn't. MPS is ideal for DSLs, it doesn't store nor edit programs as text, this presents significant usability challenges for general-purpose languages and tools. Also, MPS is not very suitable for bytecode generation, not very performant thereof anyways.
May be you can push for MPS to improve to the point this would be an advantage. All IDE and language infarstucture automatically managed through MPS.