Mata, Kagawa, Silva is what I'd look at if I were Barcelona wanting to continue the tiki-taka. Let Iniesta play the Xavi role relying less on running and the new person play Iniestas role which they could do well.
I think they have had too much of it though, the fans seems to be against it as well as they have incredibly high standards that they like to reach from it. This year is considered a complete disgrace for them and had Messi not plummeted they might as well have been in the CL Semi's/Finals and won the league.
If Moyes had such a season we would have been lyrical about him, so there is just a different kind of pressure there.