I doubt there will be a new apple TV soon. The v3 plays 1080p content, is compatible with ML's airplay and desktop mirroring, and apple's focus is obviously streaming... not really a lot for apple to change, other than release an entirely different device?
Buy an apple 2 and jaibreak and get untold thousands of movies tv shows etc. its a whole different world. The fact that the atv3 has 1080 is meaningless because the stock programming is limited.
Just buy one. As others have said, any changes are likely to be through a software update. Can't really see what they'll do with it other than a possible minor upgrade to processor next year. Until such time as Apple bring out a more capable set-top box or a whole TV, I think ATV is staying as it is.