I was playing in a server with the bodyblock plugin and someone said this, I think it may be a very good idea: what about slowing down through enemies?
With the game being 2D this seems the right solution, the slow down gives the idea of the problems a character has with passing through an enemy, having to dribble it if it was 3D, obviously in 3D you are never in a place narrow enough for a person to completely stop you, but generally it's a bit hard to get through. Also with this there could be a stacking slowdown if more players are in the same position, or just a longer time of slowdown if the enemies are near each other as it normally happens. Also the slowdown a cloaked spy causes to enemies would be less obvious to recognize than a complete block, being more similar to the jump sound, needing attention for players to notice it. Two spies bumping on each other can still both recognize the slowdown and have an awesome spyduel as they never do without the bodyblock. The firebug (that I still don't like anymore after the addition of the fireball thing) may have the ability to ignore the bodyslowdown of everyone except cloaked spies to let it dance more around enemies, kind of a dribbling skill (it would also be an interesting movement ability in the metagame), also this way it will be perfect for the classic purpose of spychecking, the firebug will have the slowdown only with spies so the player will notice the rare slowdown more. The runner can already jump over them, so it doesn't need this. Quote may need something of the sort, I don't know.
This would be a different concept behind how the third dimension is stylised in the game, and it would be brilliant for the gameplay. Also while the bodyblock is really annoying with people at the entrance of spawn points, it seems glitchy/wrong, the slow down would cause no problem at all.
Also the sentries need the bodyblock as everything else (or possibly the bodyslowdown).