Jason Roy has already established himself as an able ODI opener, him and Hales are a pretty settled partnership, they've already amassed an aggregate of well over a thousand between themselves in little under 2 years since being paired together. Maybe not quite in the same league as De Kock-Amla and Warner (who is a head above the rest as an opener right now)-Finch at the moment. Still, more than good enough to set-up the innings for a world class middle-order.
Jonny Bairstow is an excellent counter-attacking batsmen but I think it's a case of if it ain't broke don't fix it. However it is nice that England are spoiled for choice in this respect, more than can be said for the player pool the test squad selectors are willing to consider.