Hello.
I have a suggestion for Megaman X4, with this idea we can avoid the backtracking in this fantastic game: The changes is only in the volcano stage, here you have the idea:
First: change the position of the robot, to here:

Second: increase the time that we can stay in the air and that´s it:

Optional: make that this missile destroy the wall:

Look a trick on this video:
[MEDIA=youtube]mxWwvjTvpno[/MEDIA]
Here you have a complete playtrough with only one backtracking: Volcano stage.
[MEDIA=youtube]ghic48D1s2A:1676[/MEDIA]
I hope that someone make this possible.