I've spent the evening changing the editor into something a little bit more sophisticated, it can now do Hires and MCM sprites - although I still can't edit them. I've also added C64 and Spectrum modes so that once I allow you to select it, you'll now be able to edit using those colours. Internally, its almost completely changed. before I had a simple C# List<byte> for my sprites, but now I've gone and made a nice Sprite class that contains everything about a sprite - the basic array that makes up the pixels, its width and height, and which editing system its using (Plus/4 and C64 in MCM or Hires, and Spectrum).
While this actually lets me have every sprite different in the animation sequence - even down to different systems(!), its actually a little impracticle. I suspect what you actually want is a global editing mode, so that you when select C64, Plus/4 or spectrum the whole project swaps to that. I think what you really want is to be able to load in sprites from one system, and convert it to another - as best it can. This will mean that C64_MCM->Spectrum conversion gets the HIRES version of the sprite, but it gives a starting point for editing; rather than having to do each one by hand.
However, I will allow each sprite on the same system to vary - because thats perfectly valid. So MCM/HIRES isn't a global state, but one for each sprite. This means you could create many C64 MCM sprites, and then create some HIRES overlays for them, all within the same project.
This is actually the thing that pisses me off most about editors. Theres so many dependencies. Change one radio button or drop down menu, and you have to do shit loads behind the scenes, and make sure every combination works!.... pain in the bum. However... I hope to be able to use the same basic classes in the character editing which means you should be able to edit 16x16 characters for the spectrum - or Plus/4. Internally, its stored as a simple array, but when you save it out, it'll convert it to the correct output format. Plus4 Sprites, chars, sprectrum sprites, C64 hardware sprites; well...thats the theory.