Do you know CUDA or Triton? The point of Mojo was to replace GPU kernel programming langs with a Pythonic one that was more familiar
Additionally, anyone who has seen how Swift evolved should be wary of Lattner saying "the language is mostly stable", or even "the language is released".
Nvidia is also a major contributor to MLIR, which they use for TileIR and ClangIR, so should a compatibility break occur it wouldn't be entirely up to Mojo to fix it.