At an event in the last few days Robert Llewellyn was given permission to announce that in October they will be filming a one hour episode. Bad: It's been nine years since the last episode, and even at that point the characters were starting to look old. Good: Apparently Rob Grant is back on board. http://www.ganymede.tv/atspeed/2008/08/woah-ho-ho-ho-whats-all-this
Unless they try to pretend that only a week has gone by since the last ep, that's only really a problem for Chris Barrie. Llewellyn is swathed in enough latex to get by, and the other two would have aged anyway. The only other thing I wonder about, is whether or not Craig Charles is still in Corrie. That has a fairly punishing schedule...
Except the version of Rimmer that was in the last series wasn't a hologram anymore - he was the nanobot-resurrected version. Even if they go back to the hologram motif, the future version of Rimmer in Out of Time (where they'd been using the timedrive to hop around history and have dinner with folk like Hitler) had aged, and he still had a H on his head. Presumably, since Rimmer is a computer simulation of the original, Holly could adapt the simulation to take into account elapsed runtime. There wasn't much point Queeg making Rimmer do physical exercise (I mean from the crew's POV, I know the point was that Holly was getting his revenge) if Rimmer's hologram couldn't be modified in such a way - he can also get drunk if Holly simulates booze for him. Besides, they always played a bit fast and loose with how "real" Rimmer is, especially after he got the hard-light modification. He was apparently real enough to provide a DNA template for a whole bunch of clones in Rimmerworld...
I know Red Dwarf was never big on continuity, but they totally messed up an opportunity for some character stuff for that, I mean after that episode his character was quite literally a few hundred years old.
