Thanks for letting us know. I look forward to your success in both projects!
As far as I'm aware, Golden Egg is the only publicly available Yoshi's Island
editor. It was last updated more than seven years ago and isn't open source either. Hopefully this will change in the near future.
I'm a also little curious: do you expect any overlap between your Super Mario World
and Yoshi's Island
editors? Although both games likely have very different formats, I imagine things like user interface could share a common code base.