I'm not opposed to an idea like this, if Colo goes and we could find an upgrade on Taylor (or just someone who will stay fit and not be insane that'll work too) and move him on I like the idea of having a younger cb as 4th choice as lord knows the kids need to be given a chance sooner or later or whats the bloody point.
As for Caulker or Shawcross, personally I'm not all that convinced by Caulker and would much prefer Shawcross, is he the perfect defender? Nope but if the perfect defender exists we sure as hell ain't going to get him and he is an upgrade on Williamson and Taylor in the physical defender style which could make him the ideal partner for Mbwia. Snowballs chance in hell mind he'd cost a small fortune with length of contract, English premium and the fact Stoke aren't desperate for cash.