at-will spell-like ability
While you're here: Can we please get rid of the term "spell-like abilities" and just call them spells?
3e had this thing where "spell" specifically meant "these hundred-or-so spells in the back of the PHB which are cast in a Vancian style by the PC spellcasting classes," and everything that didn't precisely match that definition had to be called something else, even though mechanically it was otherwise identical to a spell (cast like a spell, affected by anti-magic, etc.).
In D&D Next, though, one of the principles is that there are lots of different forms of magic, and lots of different kinds of spellcasters. So can't we use the term "spell" to encompass all of that?
Edit: On the actual subject of themes and backgrounds, I'm in two minds. On the one hand, I must admit it's disappointing that they'll just be 'suggested character builds,' rather than actually fun or interesting content. Why would I buy a book with new themes if "theme" just means "the 3 or so feats you choose at level 1"? New themes must include new feats, which only exacerbates the problem of too many feats.
On the other hand, build-your-own backgrounds and themes are
freaking awesome. Not for any mechanical reason (since, as stated above, it's basically the same as the skill and feat systems), but just because I can take Thievery, Bluff, and Profession:Sailor, and say "my background is Pirate." Or Arcana, Dungeoneering, and Diplomacy, and say "my background is, I am a human magic user who was imprisoned under the earth and had to become friends with the drow in order to not die."