I'd like to say I'm surprised. But I'm not.
I'm not saying you CAN'T get more stories out of the Code Geass universe. But resurrecting Lelouche, and making him the main character again is just a bad Idea. His story in the original series ended perfectly
, and this undermines it.
This reeks of executive telling the creators to extend the IP so they can milk it for more money. Even if that kills the franchise further down the line.
If anime has taught me anything, it's that bad ideas can give rise to good ideas. The opposite is also true.
I agree that his original story was over, but that also means there's a risk and a challenge in setting up a new role (or personal arc) for the character in a world where he'd have to face the consequences of his own "final" plan. The plan was good for his character, but was it really the best thing for the world? Some critics have slammed the plan as too naive, so maybe it's a good thing for the creators of the show (or movie, we don't know) to address that. And make money out of it.
It's not immediately obvious how he'd be involved. It all depends on the specifics. If they actually put Lelouch in a more interesting situation than just being a masked rebel or a would-be tyrant again, I wouldn't mind whatever plot device or excuse is used to start the process because that sort of trickery is normal for Code Geass. Good, bad and crazy ideas were always in a shifting balance.
This wasn't their first choice though. They already made one attempt, over four years, to release a new OVA entry (Akito the Exiled) set between both seasons involving different characters and directed/written by the Escaflowne/Noein guy, but while it sold decently people found it either too different or too much of a standard mecha show. That has extended the IP well enough, they could even use some ideas from it for the sequel, but there was no enthusiasm for it. The property needed another shot in the arm. If they use Lelouch as a vehicle to try different things, it may actually be a blessing in disguise.