This tool has been great so far, and I really look forward to continuing to use it.
As I approach level design and layout, I'd like to be able to smoothly transition between tilesets without a screen transition. I'm also hoping to approach my tileset production in a very clean and organized fashion, without having to have a lot of overlap.
Something that seems like it would suit this very well would be to allow multiple tilesets to be imported into a single project file. For instance, I might have a "stone structures" tileset, which I could load into a project along with "forest exterior". The tilesets could be locked to different layers, so that you could export each layer as its own matrix and stitch them together in-engine to avoid any complications.