Don't they bring in a new BM with the gear up for a new edition? Is the clock ticking?
With rules changes being incorporated into the yearly 4E core books PHB/DMG/MM, I suspect a 4.5E may be less likely this time around. (Though this doesn't take a 4.5E completely off the table).
On the other hand, there is precedence of other tabletop rpg games creating new editions relatively "quickly", such as:
Vampire: The Masquerade
- 2nd ed (1992) was release a year after 1st ed (1991).
Shadowrun (FASA)
- 2nd ed (1992) was released three years after 1st ed (1989).
d20 Conan (Mongoose)
- 2nd ed (2007) was released three years after 1st ed (2004).
Cyberpunk (R. Talsorian)
- "Cyberpunk 2020" (1990) was released two years after "Cyberpunk 2013" (1988).
Warcraft rpg (Sword & Sorcery)
- 2nd ed (2005) was released two years after 1st ed (2003).
Everquest rpg (Sword & Sorcery)
- 2nd ed (2005) was released three years after 1st ed (2002).
Perhaps one could see a 5E D&D being released relatively "quickly" if the 4E ruleset was completely broken and unusable. But so far the 4E ruleset seems to be relatively well balanced and usable without many major problems so far.
There would have to be a really compelling reason for a 5E to be "quickly" released so soon after 4E.