Ok some potential themes are:
Video Game OST - Songs originally composed for Video Games, not sure if this is too exclusive or not.
Asian Artists - Pretty self explanatory, happened once before but wasn't really a proper round as it was during the split round where half the contestants didn't play.
Experimental Music - Any song/act that could be classed as Experimental, if you have weird stuff you want to nom this would be your chance to do it without getting Billied
Featured Artists - Songs with featured artists, happened once before like 2+ years ago I think, but probably enough songs that fit for it to go again.