[IanJRedman]

Not sure if it was always planned this way South East Today's problems could have been a factor here, where as part of the project several upgrades were planned, but with the delay there it has meant that some of the upgrades could not be delayed, purely speculation but it would be the most reasonable explanation. 

Plus has it been confirmed that South is the next set to be done, we don't know for sure how many temp sets they have available to them? We could have many more months of the scratches on the Perspex on the right hand side of the set.

I have no inside knowledge, but I think the fact the temporary set has made it to Southampton (and has been standing for a good few weeks now) probably indicates it's in the near-ish future?

I think the theory you put forward - that a proposed single decamp has morphed into two, due to delays in the South East - is a plausible one.