Special tweak for melee weapons that makes them do scratch damage, until you reach X successive hits in a row, which makes the weapon do massive damage. (Probably shouldn't be available for spies.)

Yeah, I'm aware of that. I was proposing alternatives to that, that hopefully wouldn't be too broken being in a separate category than body upgrades. (Because that's why they were removed.) I'm of the opinion that they should unlock defensive upgrades for sure though.

I could see boots having their own movement speed upgrades. Probably at same price as normal, just in a different area. Also maybe give shields the option to buy power regeneration and/or status resistances (besides chance of avoiding afterburn). Or give shields a general but expensive all-purpose armor option (at least 10x what armor costs normally. I'd say 1000 per increment is a good place to start).

Any word on whether you'll be able to modify the body upgrade values for power/health based on certain equips? (Shields/Boots)

I think I recall that one happening in 9.9, because I had ridiculously tanky sniper build that was possible in one of the earlier builds of that.

Sounds like the same bug that was found not too long ago with the huntsman and bleed damage. Not sure if that ever got fixed.

Maybe a better solution to the backstab thing is an 'Apply backstab effects on kill' upgrade.

Also personally I might just upgrade that to the max without weapon spread bonus just for the fun of it. Big cone of bullets.

Eh, good points, but the intent was more 'Give spy a method to backstab later in the game' for backstab related effects.

Also thought of another tweak (for shotguns and scatterguns):
Flak Cannon:
+25% additional bullets per shot
+20% EXTRA weapon spread penalty.

Basically increases spread and number of bullets fired per shot.

Just thought of an interesting idea.... Perhaps instead of 'Immunity to Backstabs' you could buy 'Backstab Damage Multiplier Reduction' instead, in increments of 100% (with -600% negating it normally, if I remember the figure of x6 maximum health correctly). And then add a 'Backstab Damage Multiplier Boost' that increases the amount of damage backstabs do. If the multiplier on the knife is greater than the reduction on the target, backstab damage is done--otherwise normal damage is done instead.

I imagine something like this would make Kunai spies more useful beyond early game, amongst other things.

I've had crazier ideas. The biggest mashup I can think of so far is UU x10 VSH Randomizer on a Pass Time map. With VSH and Pass Time, all player weapons would get 100% knockback added to them--primarily to make it harder for the Hale to capture. With UU and Randomizer, I'm thinking having a command that randomizes you, that is only useable 3 times to start out with and one additional time per round played. Otherwise your randomized loadout doesn't change. (Still get random loadouts, but without having to constantly reupgrade.)

To be honest the only reason I'd make that would be to see how many mods I can mashup in a single game.

I'd imagine Saxton Hales would have their own upgrade choices, that are proportionally more powerful but more expensive as well.