Sick! Now that you mention a SNES style theme for these projects, I wonder if it would be possible to fit MM1-6 in one ROM and then make a ginormous graphic pack for the whole thing.
A Megaman All-Stars would be so cool! Some bootlegs have done it, some even include all 3 regions and/or Rockboard. I wouldn't use any of those as a base now though, they're just simple text lists that jump to the vanilla games. I want to use MM3 Improvement as a base for MM3 as well as other minor graphical hacks to the rest of the games.
That said, it probably wouldn't be too difficult to transfer most of the graphics from the standalone ROMs to the All-Stars version, either. So long as the palettes and pixel placement of each tile stays the same, it should be fine, at least it was for my MM1 pack, which is why it works on all three regions with minimal effort.
The only problems I see are:
1. Renumbering the sheets in hires.txt. Each sheet is numbered and must be numbered properly to work. Mesen handles this itself normally, but with my MM2 pack, I'm dumping things with one ROM and transferring the work to another ROM, where each sheet is named and organized in a logical way. This makes changing or referencing back to other graphics MUCH easier. Mesen just numbers sheets "Chr_0", "Chr_1", and so on.
But to combine multiple hires.txt files, 150-250 sheets per-game would need renumbered and added. MM1 also needs organized like MM2 at some point.
2. Any reused graphics would need accounted for. I don't think anything other than Mets was intentionally reused, but there could be very simple graphics that appears in multiple games.
PS, finished importing Crashman's graphics tonight. I don't like the pipes, I spent way to much time tweaking the palette and never found one I like. They get darker as you play the stage. Totally open to a different palette and let me know what you think of the lines in the sky. I just tried it out to break up the solid blue a bit.