Hmmm, well I'd imagine he's going to be starting work on another big project for Turbine, and only poking his head in on others. To be honest he's not really "right" for their existing stable.
DDO isn't an "open world" game, when I played it, it was more of a giant hub where you departed from one area to another to adventure zones/modules with a team, and those were generally pretty linear. It was an approach that worked, but it wasn't like being able to just head out and go tromping accross the landscape of Eberron like you would with Azeroth or Norrath.
LOTRO is a tradtional MMO, but it's also one with a style that seems fairly opposed to what Rolston does. He's a high fantasy guy, and probably has some respect for the work and might even be a fan, but his successful work like "Morrowwind" and "Oblivion" has had a fairly differant vibe to it. "Amalur" was okay, but as the debacle shows it was at best a moderate success in the big picture.
I'm sure his name will show up in connection to some tweaks here and there, but I'd give it 2-4 years before we really know what they wanted him for.
To be honest I also wouldn't be surprised if Turbine is engaged in a sort of "denial of assets" strategy. That's when companies hire up valuable employees for the simple reason of preventing the competition from using them. Turbine runs two solid, but hardly blockbuster MMOS, a couple of the lasting "also rans" which more or less crawled back from the brink due to the free to play model. It's fighting companies like Perfect World (which has Cryptic), NC Soft, and others for this niche. I could see why Turbine might be willing to pay Rolston and give him a fancy, undefined, title and few actual duties, just to prevent Perfect World from grabbing him for "Neverwinter" or whatever, especially seeing as that's going to be going directly head to head with DDO when it comes to D&D fans, and also carrying a more popular setting (Forgotten Realms generally has a bigger and more fanatical fan base than Eberron does, a slight expansion into Faerun won't offset this I don't think).
I'm not saying I know anything, that's just my speculation on a lot of levels. We'll see what happens, it seems most likely he's heading up a new project though.