My bad, flipped the bit in the wrong direction when unifying SVE and Neon text for the proposal. Reverting.
Thanks, after looking a bit deeper, this seems like one of the classical tradeoff between “passing static information via a) type, b) attributes, c) op semantics or d) structure in the IR”. In this case, the problem seems to clearly favor op semantics. I imagine it involved some considerations at function boundaries but signed/unsigned/signless have the same size so maybe the considerations reduced to nothing.