Ghost Rider and Iron Fist haven't met too often, especially not the John Blaze version. I vaguely recall a MARVEL COMICS PRESENTS story in the 90's where the Ketch rider teamed up with Fist to fight something, but aside for that, nothing. It would make little commercial sense to merge the two into one title. A back-up strip only makes sense on a book that is actually selling a decent deal better than the book being canned. INCREDIBLE HERCULES, for example, usually sells 5-10k better than AGENTS OF ATLAS, so it makes some sense for the back-up. The goal is to keep AOA lively while maybe adding an extra few thousand readers to IH and justify a $4 price tag, which will allow IH to bring in more revenue in the short term. In August 2009, two issues of INCREDIBLE HERCULES sold 32,000 copies and 27,000 copies for the second, while AGENTS only sold barely over 20,000.
IMMORTAL IRON FIST and GHOST RIDER, though, are not selling well even with their "hiatus" mini's. GHOST RIDERS: HEAVEN'S ON FIRE #1 sold under 22,000 copies; right about where the ongoing series was selling, only a buck more expensive. Fist ended not far behind that. The two merged would be lucky to sell 30,000 copies at DEBUT.
For Iron Fist, the time for a proper HEROES FOR HIRE series is a bit overdue. Luke Cage may still have some rep from NEW AVENGERS, albeit not as much as he may have had, oh, four years ago when it was really "new" (a title that is almost 5 years old is hardly new). Now, I've liked the IMMORTAL IRON FIST series and the focus it gave to Rand, but it's hardly like Luke Cage or the Daughters of the Dragon were especially absent from that book; they were still the regular supporting cast there about as often as Orson Randall or the other "weapons". They just weren't on the title.
As for Ghost Rider, Jason Aaron's run is coming to a close and I am hesitant to remain on the book without him unless I have faith in whoever is replacing him. They launched that title in the wake of the film and after saving Heaven the Rider might need some time to refuel before another launch.