In the age of the internet it probably doesn't make a difference which movie gets the trailer, whereas in 1999 there was a night and day difference between watching the TPM trailers online (or even on tv) and seeing it in the theater.

Now it's more about timing everything perfectly and building as much social media buzz as possible. Also, people get pissed when they go see a movie expecting to see a trailer and it never shows up.

It would certainly be more appropriate to put the teaser out with The Hobbit. Ep7 opens on the release date that has been occupied for three years in a row by The Hobbit (and shall be for three years after that by the Avatar sequels, although the first Star Wars "spin-off" is opening within only a week or so of Avatar 2). Battle of Five Armies is definitely the big end of the year event movie, just as the other five middle earth films were. If they're looking for as many eyes as possible to show the trailer, they've got The Hobbit. If they value corporate synergy more, there's Into the Woods.

ETA: Ah, TORN. That and TFN were my one stop locations for LotR and Star Wars news/rumors/spoilers back in the day.

I keep hearing these rumors about a Batman v Superman teaser hitting next month. It's not impossible, but it's the definition of wishful thinking. The movie will still be 15 months from release.