They have not been confirmed, far as i know. So getting excited is rather pointless.
Someone found files added from a recent patch referencing crossbow animations. I don't think they would throw stuff like that into the game files unless they are planning something serious. Also, a little off topic, but it is pretty much confirmed that TESO will NOT replace the traditional numbered entries. Pete Hines has said this a couple of times already on Twitter.
Now back on topic, I find the idea of crossbows making their way into DLC welcoming, unlike a few people who for whatever reason think that crossbows should never be a feature in a TES game ever again. Why anyone would hate crossbows like that is a baffling mystery in my opinion. Crossbows would only add variety and potentially replayability to the game, not harm the game, at least something like that isn't
supposed to harm the game in any natural way, anyway. I'm not accusing anyone here of anything of course, but I have seen people make posts about why they think crossbows shouldn't be included in Skyrim, and it really doesn't make much sense to me other than the fact that they haven't been featured since Morrowind.