Foster being left out is a joke, absolutely brilliant gloveman and a more than useful batsman to have in the lower order. Plenty of innovative shots and scores quickly. Can turn a match on its head with a brilliant bit of glovework or a series of boundaries late in the innings, not sure what else you want from your keeper in T20.
Wainwright could be useful in the West Indies tbh, pitches are going to be slow so you could see two or three spinners (four if you're Zimbabwe
) bowling in an innings quite regularly. Wainwright has a pretty impressive economy rate as well IIRC.