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.