Well, actually, a recumbent tandem. I have designed a bike with frame couplings that will quickly pack. My problem is that I have no prototype, so I don't know how long the tubes should be to prevent knees knocking against seats and other nuances of the build. I have designed in a lot of special features that prevent me from simply putting couplers on an existing tandem. I know of an overseas builder who is willing to tackle it, but they need very specific measurements.
I could also use local suggestions for one-off builders that would find a project like this fun, as that would make more sense to me than sending drawings off to another country.