I think that rusc still has room for improvements wrt tuple trait errors. I think there are only a couple of patterns for performing generic variadic type gymnastics. Maybe if you point out what the missing link was, we'll be able to come up with an error pattern that can find and point out those sorts of missing links.
I was sort of in the same boat, but we found better errors messages without needing user defined errors: Better user-definable error messages
We probably won't be able to fix it all the way, but Im guessing other things run into the same type of ugly messages.