Why would you need CHERI if you have working mitigations that don't demand a second bus?
I think it's two halves of the same coin and Apple chose the second half of the coin.
The two systems are largely orthogonal; I think if Apple chose to go from one to the other it will be a generational change rather than an incremental one. The advantage of MTE/MIE is you can do it incrementally by just changing the high bits the allocator supplies; CHERI requires a fundamental paradigm shift. Apple love paradigm shifts but there's no indication they're going to do one here; if they do, it will be a separate effort.
I think it's two halves of the same coin and Apple chose the second half of the coin.
The two systems are largely orthogonal; I think if Apple chose to go from one to the other it will be a generational change rather than an incremental one. The advantage of MTE/MIE is you can do it incrementally by just changing the high bits the allocator supplies; CHERI requires a fundamental paradigm shift. Apple love paradigm shifts but there's no indication they're going to do one here; if they do, it will be a separate effort.