I'm just going to sit down and wait until more details come out.
This doesn't have to mean a sequel directly following R2, there are far more possibilities available, inside or outside the established universe.
I wouldn't mind a complete remake of R2, but that's probably unlikely since the ending per se, at least according to an interview in Continue Volume 42 with Okouchi (the main writer), was close enough to what they had originally intended, in spite of everything else. On the other hand, in that same interview he didn't rule out the possibility of a sequel but did point out how difficult it would be to bring all the same staff back together again.
Gundam 00 has, for all practical purposes, stayed within one same time slot all along. It only moved from Saturday to Sunday because the entire programming block did. In other worRAB, the show pretty much kept the same audience and I don't think anything had to be changed between seasons, or at least nothing out of the ordinary.
In the case of Code Geass, what GWO said is right, but to be more specific...the staff couldn't directly continue with their original plans. The show couldn't pick up right after the cliffhanger end to season one because they couldn't assume everyone who tuned in would be up to date. That means having to come up with an excuse for the time skip and writing a new scenario around it, which wastes time that could have been used more efficiently. There's also the likely fact that Sunrise wanted to commercially exploit a show that was unexpectedly successful (in terms of sales), as opposed to Gundam where I suppose all the commercial demanRAB and requirements are part of the plan right from the beginning.
As for content, that's not the big deal, but the violence was in fact slightly toned down in several places, as a comparison between the Japanese broadcast and the DVD/Adult Swim footage shows, and while the fanservice may have increased in quantity it also became less explicit (less nudity).
I will admit, however, that the staff is still ultimately responsible for their own decisions and they could have adapted to the new time slot in a better way, but that's just speculation.
There are actually several specific sources for that, most of them in Japanese but with some English translations available. I thought about quoting some of them here, once again, but decided to keep this short. To list a few, there's the Taniguchi (the director) interview in the Roman Album for season one, the Code Geass R2 DVD/Bluray Booklet 1, and the interview with Okouchi in Continue Volume 42.
