Requiring *all* blocks to be made within a 1/4 second time-frame is something that might actually add considerable depth to the game. There would need to be severe rebalancing done so that an opponent can't simply sit with a chambered sideswing held to your side, though.
Aside from your given example of a guy holding an attack direction for a million years and microholds, this is pretty much the time that people already block in; otherwise they take the hit.
A change like this - something that cranks up the learning curve of the game, and potentially adds a large amount of depth to the game - is an example of a good change.
Remove manual blocking, shorten player-hit stun animation. Skill ceiling skyrockets, depth variable. Alternatively, you can add a 1/10 to 1/8 second manual block so 2-direction weapons aren't useless beyond highly coordinated teamplay. Shields could be 1/3 second, I guess.
Then again, my opinion is probably shit, so whatever.