The other side of this approach is that when the mainline developers do not have much love to a particular platform, it is dropped altogether with little to no

The other side of this approach is that when the mainline developers do not have much love to a particular platform, it is dropped altogether with little to no remorse - see the fate of Microblaze support, or even the good ol' C backend. I wish we had a more stable API (maybe with a transformation layer) for the backends that may not probably need much of the new features. If LLVM had a maintained transformation layer from the "current" SelectionDAG to a stable one, it would have helped a lot.