Yes, I think it is. I've become interested in typed throws because it's a good direction for error handling in Embedded Swift, and have started on an implementation.
I'd be happy to work with other folks on the proposal and design. @minuscorp had a good start on a proposal that captures a lot of the motivation, and @John_McCall laid out much of the semantic model. Those would need to come together to have a complete design to make its way toward review.
Doug