This is really awesome. I hope it becomes a viable alternative to Lunar Magic in the not-too-distant future.
You should also reach out to p4plus2 as he was also developing an open source Super Mario World
editor a long time ago. I don't know if the project is on hiatus as he hasn't mentioned anything about it in a while, but it wouldn't hurt to talk to him for ideas. Hopefully he's still working on it "behind the scenes."
Also, your download link is missing a "url=" parameter. It should be: