Hmmm, is this using the Private iCloud Database/Container feature by any chance?

If so, I wonder if you'd get a warmer reception if you explained this. It's an interesting feature of iCloud that really isn't replicated anywhere else and is actually very cool.

I considered building an application like this awhile back when I realized how you could make the invitation links cleaner than the default ways iCloud handles it, but the landscape felt too crowded for one person. I like the design and approach though - good luck!