Well, apparently anything goes these days, so Soldiers and/or Demomen may get to trade in one of their weapons for an object that protects them from self-damage.
Soldier getting a melee replacement that lets him dig foxholes or otherwise create some kind of cover is seeming more and more likely. This would create interesting teamwork opportunities, and we all know how awesome those are. Maybe: attack the ground with the shovel to get a sandbag, then drop it wherever you want, and it'll persist until it takes a bunch of damage. Stack them on top of each other! Drop them on unsuspecting enemies! You can't repair them, though. Enemy melee attacks do extra damage to them, and you can break them down quickly with your own melee attacks (allies need not worry, since they can pass more-or-less through them, much as how your allies, but neither you nor your enemies, can pass through your own dispensers).
Since they are doing more things to make Pyro situationally useful, I bet you'll be able to spill the bottle of scrumpy on the ground somewhere, then any flamethrower, flare gun, fire arrow, or burning person that lands in the puddle will make it burn for several seconds, with any enemy that enters the area being set on fire and taking damage. Maybe you can deliberately break it with an alt-fire or something, and it repairs itself over time a la Sandman and Jarate.
On the subject of upgrading melee weapons, give the Medic back his huge comedy syringe. If he hits an enemy with it, it will fill with blood; if it's filled, he can attack an ally, or alt-fire to attack himself, by injecting that blood to give an instant full overheal. This, of course, empties it.
The alt-fire on Heavy's fists makes him grab an enemy and toss them: basically it immobilizes them both for about half a second, then whatever direction the Heavy is facing, he flings the enemy through the air (the target class' weight determines how far they'll go). Not to leave the KGB out in the cold, of course - an alt-fire with them causes him to slowly and comically wind up a mighty punch which does extra damage proportional to the reduced rate of fire. Not a taunt kill, though, because he can still move while the animation is going. And it's not that strong and slow.
Kukri alt-fire is a slow attack that pins an enemy to the ground or a nearby wall, if one is handy. For several seconds they can still attack, but not move.
Either baseball bat gains the power to deflect projectiles, though the timing is of course extremely tricky.
The fire axe: ...?
While we're at it, maybe an update that can accurately track whom to credit when a physics effect knocks somebody down a hole.