Thomas went to Demonreach for some purpose. I have no idea what for. It could be a way of keeping him alive in case he is needed or it could be a way of freeing him from his demon. Or it could be a way on introducing the unknown prisoner with the faux accent.
Harry took Thomas to Demonreach for a few reasons that I can think of. First and foremost was to keep him alive, the second was it was the only way to buy time during a crisis where he was clearly needed elsewhere. It was also the only possible political acceptable solution that all sides might go along with until the truth of what really happened could be sorted out and justice decided. I think it could lead to Thomas being cured, but not at all as he was, remember Harry's vision of him in Blood Rites in the soul gaze.
It might be something dramatic like Errol Flynn playing Robin Hood or Captain Blood. Captain Blood is better. Thomas comes off better as a pirate than a merry man. Thomas saves Mr. Etri's life or the life of a family member or several Swartalves. I'm not saying Thomas will appear as a KotC, though I suppose that could happen too. However it happens, Thomas will do something that literally balances the scales in the Swartalves eyes. If she's around, Mab may be impressed as well; setting up, or at least suggesting, Thomas as the next Winter Knight.
Actually I wouldn't be shocked if Thomas did end up of as a KotC. Think about it, where is the Sword of Love located? Tucked away safely with the rest of the Artifacts on Demonreach. Where is Thomas? In cold storage minimum security on Demonreach..
Here is the scenario;
Alfred informs Harry that the Hunger Demon has been removed from Thomas and will remain safely locked away with the rest of the demons and monsters. Harry lets the now ordinary vanilla human, Thomas out of his cell. Thomas is now the slight bespectacled human Harry saw in his soul gaze who was struggling with his Hunger Demon reflection and losing. Thomas still loves Justine and wants to save her. Harry calculates that the only way that she can be saved from Nemesis is with the intervention of a KotC. Harry is still Sword custodian, still has insight and say as to who gets a Sword. Because of his love for Justine, Harry determines that Thomas should get it, the Sword lights up in agreement.. New Knight Thomas, out to save Justine and the rest of the world...