In all honesty, I think porting different versions of the same tileset is somewhat a waste of effort - not to mention it ends up looking like quite a messy end result. I'd think it's better to put effort into new tilesets. (To be fair, the Master System versions often have actual differences in terrain / etc, unlike Genesis / EGA / etc which are literally just recolors and if anything should be alternative display options user-side than seperate tilesets.)