Good idea but I think sprite editor isn't needed.How about A map tool, like advance map, but for Gold/silver/crystal, Goldmap does not work very well, and It cannot change the tile graphics or the links to other areas (note, Crystal has diffrent coding for maps and larger tilesets), it may take a while, but I know you can do it
Also a GSC Overworld Sprite editor that can edit all the overworld sprites in GSC, for all 3 versions
Pokemon Gold Sprite Editor can already change almost sprites in G/S/C expect girl-hero.
EDIT:
I still think you should create a worldmap editor for G/S/C which could also change the locations of places ;)