I don't oppose to this specific change, but it feels like another sign of the fact that using VSIR both for disassembling and as an internal IR is going to be more and more complicated. In particular, with this change if you look at a `dcl_constant_buffer` instruction you don't know what's the actual size unless you know which SM you're using, which I don't find a very desirable property.
I agree with the general sentiment, but note that there's no inconsistency on the vsir level; this is a change purely to the output format. And while shader model 6 d3d-asm is a format invented by us, there are certainly shader model specific d3d-asm changes that are out of our control, like those between SM3 and SM4, or those between SM4 and SM5.1.