The guys at Legit Reviews have taken a look at new i7 NUC that is supposed to be shipping in April.
The thing will feature an Core i7-5557U processor and Iris Graphics 6100 GPU. TDP is pushed up to 28 watts. More CPU and GPU power means this might even be able to do some more than basic gaming, whereas the i5 model remains a bit limited in that department still. Only available in the higher case version that fits a 2.5″ drive.
The i7 version is touted to be 4k ready, but actually the i3 and i5 versions do also support 4K resolutions (even @60Hz). 4K gaming is probably out of question with any of these NUCs.