I vaguely suggested this in GS's thread about Barret's controls.
This is a good idea in my opinion, despite Barret or Megaman's personality, the option could still be available for "the player" I mean, there are some persons that use to think carefully their moves before striking, what about if the player is low of health? he could sneak to avoid fighting a very dangerous reaverbot.
Good examples of how to implement this idea are:
Xenosaga Ep. 1: There were some enemies that only could detect the player by the noise of the characters's footsteps, the player could avoid fighting by just walking, even if the enemy was near the character.
Tenchu: Stealth is the main point in the Tenchu series, because the characters are ninjas, so the sneak skill is very complex and real, an enemy can spot the character when the player lands of a jump (the noise can be diminished by crouching or rolling at the time of the landing), running on water (again, the noise is less if the player walks or avoid steping on water) while jumping into the water (if the player enters the water by rolling on the ground the guards can't hear the splash) and so on, the game is very creative in this aspect.
If this feature is included in the final product of course it will be far less realistic and complex than in Tenchu, maybe it will be used just for the above mentioned purposes, if you think about it, in MML there were no real uses for walking, except for that small and plain tutorial in MML1 that Maestro mentioned, the feature IS there, but it's almost imperceptible and useless, so giving the walking function a plus, even if it's just for the player's fun is ok, but implementing a bit more creative it could be something the player could rely besides shooting and punching.