Thanx Omaha. You're right. I'd forgotten that. (Though I now recall that I always thought/hoped that Dorian swiped it from Cap'n John, rather than Cap'n Jack.)
Either way, both Jack and River are time travelers, utilize the same time travel technology, and have very similar personality types. Pairing the two together seems a no brainer, and would seem to have a lot more potential than a single adventure would do justice. I say giving them a series is the way to go. Either reboot "Torchwood" and bring in River to replace one of the characters from the original run who got killed off, or give "Torchwood" up for dead, and simply give Jack and River their own spin-off.