Recent years have seen other parts of the Fremantle empire undergo closer integration with aquisitions seing their names being disbanded in a spate of debranding and mergers to create country-wide operations. Even big names like Grundy Television in Australia were not immune from this process.
The decision to demerge operations here (even if it is only a branding excercise) would appear to be a bit strange. Unless there has been a wider change of heart at Fremantle and this is likely to be repeated elsewhere with retired brands being brought back, I can't see this arrangement lasting too long.
The company FremantleMedia UK takes over from Talkback Thames. It's merely the departments that will take the Thames, Talkback etc names. So instead of simply been called entertainment dept, it's now Thames.
I don't know any more than you but each Fremantle operation has its own head, and one of their biggest deals is the UK Talkback Thames. Sara Geater is in charge of this, and as CEO I would assume this move is down to her with input from Fremantle. Their worldwide headquarters is London.
I've been following the changes in general for Talkback Thames and it would seem this comes about as a result of a root and branch review of the business after their most lucrative order, The Bill, came to an end. I doubt it is one of those random brand renewals to be forgotten about a few months down the line, on this occasion.