A while back FFG announced they were going to release a "wave of expansions" for ToI starting with the Designer Series Volume I. This would include sets of new tiles and terrain boards as well as "reinforcement packs". I can only assume that the Map Upgrade Pack is part of that wave.
On a related note, the "reinforcement packs" would have contained 5 World Tank Museum models plus new cards and a new scenario. The first WTM models were going to be from the Kursk set. However, FFG dropped WTM from their distribution line so I imagine that idea has been scrapped. I wonder what happened to any of the proposed cards and scenarios? It would seem from the description that at least the cards found their way into this new Map Upgrade Pack.
Here's some additional information:
It has the same quote that Pilfer posted, but goes on to say:
"Also included is the cardboard from the base game with upgraded obstacles such as tank traps, bunkers, and hills, giving players much more flexibility when creating custom scenarios and recreating famous battles."