I wouldn't mind seeing it. There were circumstances surrounding both fights that had a clear affect on both of them (though, personally, I think it's pretty clear that Shogun's circumstances had a much larger effect on his performance than Forrest's did, not that I'm diminishing Forrest circumstances), and they're both clearly not in their prime anymore-- though Shogun is still more physically there than Forrest is-- so it could be a very interesting fight. Forrest is just a little bit slower and weaker than he used to be (he was never very fast or strong in the first place, but he still slowed down a bit), and he's lost that "never count Forrest out" factor that he had in his prime that led him to becoming one of the best fighters in the world. Shogun, obviously, has had a lot of physical problems and his cardio and complete fighting style-- his kicks, knees and pace, mixed in with his punching power, has been replaced by kicks, knees and punches for a round or so, followed by overhand rights and looking for a one-punch KO-- has suffered because of it; he's just looked like a faded version of himself in his last couple fights.
It could be a very interesting fight. I think the result would mainly be one of those things like the Tito Ortiz-Forrest Griffin trilogy, though; there would be no real clear winner of the trilogy as a whole.