I clearly understand your suggestion to replace the Maneuver level with an appropriate Martial Lore check, but my goal is to avoid epic-spell mechanics by improving the previous level-based system.
In the normal level-based system a Martial Adept can learn a Maneuver of a specific level only if it has a sufficient Initiator level.
The mathematical progression imply that one can learn Maneuvers of a level equal to half his Initiator level (as per Table 3-1 pag 39 in the ToB).
Levels from 17 to 20, although, break the previous mathematical progression by giving access only to a single new level of Maneuvers (the ninth).
I've taken this "discontinuity" and turned it into a new pattern for high-level Manuevers.
Initiator Level_____Maneuver Level
and so on...
Additionally a Martial Adept must take an Epic Feat similar to Improved Spell Capacity to unlock each new level of Maneuver beyond the ninth (obviously the Epic Feat has an increasing Initiator Level prerequisite that match the table above).
Given that, my biggest problem is to balance the new Maneuvers, avoiding over and under-power.