I don't mind themes if they're not too specific. So for example I don't like it when they have to sing a song by a certain artist. If it was say "90s" or "love" then it's not too bad as it doesn't favour any contestant.
I can't see them ditching them though. This week will probably be Halloween, which some contestants will get round by simply dressing up and then singing what the hell they want.
Edit|: Ah just seen the link above, no Halloween theme then, lol. Good - because there are literally only about 5 "scary" songs.