There will be a ZT3 in the future. Its a very profitable franchise that BF wouldn't hold on to without developing. If they're going to move in a new direction with console-friendly games, and start a new title for the series, then I highly doubt they'll sit on Zoo Tycoon when they could easily sell it to another studio.
I think I read that they're holding the rights through 2009 (but don't quote me on that), which is not enough time to develop ZT3 from the ground up (I don't think - especially since there's no formal ZT3 team assembled), but certainly enough time to keep packing content in to ZT2 with an end buffer.
I think Blue Fang did a wonderful job with ZT2; I play quite a few computer games from a wide spectrum of genres, but I keep coming back to this game time and time again when others get stale. But if they feel that they're creative energy moving in a different direction - say, for example, a game where its more about detail animal care instead of overall zoo design - then in the end, that will make a better game, because they're doing what they want. And if that happens, and they sell off the ZT franchise to a team willing to breathe fresh air in to it, whilst holding on to its classic gameplay, then I think that'll be the best end result for .. well .. us
Not just because we'll have two different Zoo sim styles to choose from, but also that neither team would feel forced to compromise their vision.
=Apt42=