on the engineer topic... I'm hoping they give him alternate buildables rather than weapons as they are his main arsenal. Here's my idea for a Sentry Replacement
Mobile Turret:
-turret that requires a player "man" it. It has no automatic aiming or firing, this must be done by the occupant. Any team member may man the turret, but the engineer can only repair it from outside the turret.
-Turret has it's own weapon that the occupant fires, and must be reloaded with ammo by a engineer
-Turret has 3 upgrade levels, each increasing the firepower
-Turret is able to be moved by occupant, Level 1 about the speed of a heavy (while he's firing), Level 2 would reduce the speed further to 1/2 the speed of level 1. Level 3 renders the turret immobile, sacrificing the mobility for added firepower.
-Sapping the turret disables its weapon systems, renders it immobile while the sap is active, and locks the door trapping the occupant inside.
-Turret protects occupant from harm while it is in operation, should the turret be destroyed the occupant is then able to walk away from the wreckage to fight with is own weapons.
I think this could be interesting, obviously it would need balancing, but it would give the engineer more of an offensive role. And since the turret would have to be aimed by a player, wouldn't be as good at defense as the sentry as it doesn't have the reaction time and can only see in front of where it's aiming. I'm not thinking anything tank sized, more like the size of the payload cart.
Also, what would help this concept would be to give the wrench an alternate fire that would lower a buildables upgrade level, so you could charge in, upgrade your turret to level 3 while you're on the objective, then downgrade it and move on.