The concept is close to something I have imagined as well. I'm intrigued someone is working on something like this for RMSS/FRP. In fact, this could be a major part of some kind of Arms Companion for RMU. The fact that high skill bonus never really increases attack speed is annoying.
For that reason I use breaking 150, originally from RoCoI or II, I don't remember exactly - if you score 275 after db is subtracted, I lookup a 150 result and then apply the surplus again - usually in a new attack versus same target, but I subtract db again except from parry, that only applies once. If the first attack downs the foe, I allow the player to select a new target if this does not require much movement beyond 1 hex or 5 feet So 275 after db and parry, vs foe (with zero qu bonus) and normal shield, results in new attack@125 minus shield bonus, net result of 100. In this case the second attack probably doesn't do much, but it would with a 350 result.
I've long imagined a whole barrage of Combat Maneuver skills though, exactly along the lines Cory is scetching up, but never came to the point of actually writing a draft. However, I do this:
Minimum activity for a melee attack is: 60% for rank 1-10, 55% for rank 11-20, 50% for rank 21-30, 45% for rank 31-40, etc. This enables a character with a lot of ranks to strike in more than one of the respective action phases, but with a penalty for attacking with less than 100% activity according to the rules.
Weapon styles per MACo does provide a few options. though.