I don't see any push to make RNP AR approaches with lower than CAT 1 minimums so it will be a while before ILS or MLS will be bettered.
My original point was about comparative cost. The point about the chicks needing the same capability is a good one as I don't know what kind of Nav kit they have as standard but for the AT fleet you have 3* with 3C capability and your own sim. The only thing missing is the will. I'll bet the C17s have low vis capability too.