If you have any interest in perhaps using JSIL to cross-compile the .NET components of your engine, send me an email. It seems like it could simplify the maintenance of your web player (by eliminating the need for some code duplication). You could potentially consider moving the editor into the browser too, but that's more work.
Anyway, this seems like a great tool. I like your emphasis on collaborative editing - too few tools consider team workflows; some aren't even compatible with revision control!
Thanks for the offer. I'd love to move the whole platform to the browser in the future, but I'll probably wait for WebRTC and WebComponents support to get better before I start looking seriously at it. If I find the time, I'll try to see how a JSIL port of the Web player compares to my handwritten approach, I might be surprised to see the result :) Thanks for the pointer!
Anyway, this seems like a great tool. I like your emphasis on collaborative editing - too few tools consider team workflows; some aren't even compatible with revision control!