How It Should Be Done:
I'm hoping the way I'm suggesting it can be detailed into coding so that if the devs consider this, they can at least be able to better transpose the idea to best fit what I'm trying to suggest.
There would be a simple 8x8 tile in which users can drag and drop onto the editor scene. This 8x8 panel can be expanded to be able to fit dimensions as needed within the map editor itself. Users have two important properties to access with these tiles. The first one, being Grayscale Enabled, a boolean value which allows the tile to be subject to the coloring. The second, Edit, which will open a standalone MS-Paint Type program with a canvas with the same dimensions as the placed tile. If grayscale is set to true, program will limit the user to only drawing using the grayscale pallete (or essentially setting R, G and B to 0 and locking them from being moved).
Users can then draw whatever their heart desires (Hopefully in an art style akin to that of SFD).
When closed out, each pixel is sent then as what I can assume is processed pixel by pixel as a 2D Array, then placed into the position in which was drawn and shown on the map editor. It should save internally within the map files so that users will not need to require the map like in the old days... (*cries quietly to self*)
Important Features to Consider:
- - Standard Spriting tools found on MS Paint (Y'know the ones that really matter like lines, boxes and other such).
- Set a Transparency Color (This can either be a single, spesific color, or just have the standalone automatically process a transparent background).
- Copy/Paste (Because users will want to copy the fantastic art of others as usual).
- Export as .PNG (Or whichever HQ image file is easier for XNA GS to convert to, helpful for having a backup image).
- Import from File (Another helpful way of inserting images from a backup)
Custom Assets are not only a way to cut down on the amount of space the game requires to load tiles, but it can also be easier for users to add additional detail to already current tiles. No more need for signs (and all respective tiles affiliated with them), billboards, and most of the far background tiles! Giving users more freedom to work with will encourage users to make more unique maps.
I'm sure you'll find that the effort put into adding this feature now, will have a much greater payoff in the end, decreasing the stress of loading map tiles as well as freeing space for additional features to be added into the game.