what engineers will be able to do in the next expansion, such as building siege weapons and other such machinery. You've probably already heard that engineers will be able to craft flying mounts, but other than that we haven't heard so much.
Other posters got pretty creative too, though. There were suggestions of more goggles, more pets, more fun trinkets of course, but one suggested that we make remote controlled planes that can shoot each other down. Another person suggested that there be little remote controlled machines that could sneak past enemies and scout about or throw an optional switch in an instance.
The obvious thing that somehow didn't happen with the Burning Crusade, is just to provide upgraded versions of existing trinkets that actually help as much as the old trinkets did, a Gnomish Battle Piglet, perhaps, or a Goblin Gnome Launcher. One poster to the forum thread said Engineering should be a bit on the overpowered side, and I agree wholeheartedly, especially since many of its items can't be used in Arenas.
To my mind, it should almost be like a secondary class unto itself, with lots of different abilities, from crowd control to healing -- nothing as powerful as a native class ability of course, but something to make engineers feel really glad for choosing their profession and putting lots of work into it.
One of these days, Blizzard has got to listen.