The only reason I think PB would have a hard time returning to the Gothic IP is where the story left off at the end of Arcania. I do not think it would be easy to pick up from there, as they made the nameless hero a pretty passive NPC by making him the king, along with most of the other characters you could care about in the series. I rather doubt they want to pick up the story of the Arcania (horrid emo hair blunt uninteresting dude) protagonist.
So how would or could they contiune? Probably by a huge retcon, cutting parts of, or all of Arcania: G4 and probably even Forsaken Bugs. I personally don't like that idea either, but PB is known for being a developer that used rusty axe cutting and retcons in their history (Risen 2, for instance).
As for Arcania, as much as I was one of the people who were really looking forward to it, the game sadly failed to engage me at all. Despite the familiar characters, the story was a total mess. They introduced some elements that did not work, upset the wonderful mythology of the Gothics and failed to present anything remotely interesting to me. Endless corridors in huge empty scenery with monsters running at you and you just click click click them to death. I remember the game being a torture by the second half, I wanted it to end. No small interesting nuances, no living settings, no sidequests, nothing. I never ever want to replay it, and that's quite telling (I have replayed the Gothics, even FG (!) several times, and the Risens, too).
As for Spellbound, I would love to see a new Commandos clone they make, because in those games, it seems, they could find something they could put their passion in. I remember all the small bits and stuff you could do in Desperados, now THAT was a game I would want to go back to.