I predict that before long, all desktop distros will adopt a rolling-release model. Maybe they will update the plumbing only in set intervals. But all the user-facing stuff is developed in a speed which makes a period of several months between releases seem unsuitable. This is most apparent with web browsers, where Mozilla and Google have a release cycle measured in weeks, not months.
If I understand correctly, Fedora is already a partially rolling release today (the kernel package).
It becomes kind of a matter of semantics. Simply put, we update 'stable' Fedora releases to the latest stable upstream kernel, we no longer leave them on the kernel branch they were on when they were released. F16, F17 and F18 are all on kernel 3.6.5 right now.
We do the same for Firefox too, we follow the upstream releases. It's not feasible to do anything else, really. F16, F17 and F18 all have Firefox 16. We don't officially package Chrom(e/ium), so that's not a problem.
Fedora already supply's an up to date kernal about a week after a new one's released. It also sometimes updates the gui and the web browser. Basicly, by default it's as much of a rolling release as opensuses tumbleweed ever was. As an ocasional fedora user it seems like it already updates the things i care about. Bigger changes i can comfortably wait six months for for the sake of stability. I understand someusers may have had bad expiriance with fedora and I'm not currently an active fedora user but i can't think of a single issue I've ever had with fedora (might be my poor memory) in the past... other than it not working with my proprietary printer driver, which is why I won't put it on my laptop. Basicly, for my hardware at least, things seem good the way they they are.