Why do you think the screen sizes will change? Anything larger than 27" could cause problems on peoples desks.Two more years or so, then we may see a 23" and 32" inch retina models.
Nothing different case or screen wise until 2015. Cost is too high for those panels.
i dont know about retina but is for sure that we will have the new 750M , 780M graphic cards and with the new wifi ac
CpuS should lower noise i hopeThe graphics would be worth the wait, but the AC wifi is nothing to justify waiting for, especially given my NSP router is still using the N protocol.
21.5" is too small if you ask me. 24" is much better.