today WG staff has been very active in the forums answering questions (mostly about the December specials) and I compiled some information that found interesting/helpful:
-When the sentinel appears its likely going to be a permanent sale item in the premium shop in a small package with its 100% BIA crew, and AUS customization + possible undecided unknown other content. And not in game.
It's "currently" due mid December, but not fixed enough to consider fully confirmed yet.
Sentinel AC 1 statistics.
-The new IS-3 is a Autoloader in real life however it does not have a clip in game.
Player: "IS-3 Autoloader" WG: "Please don't call it an autoloader"
-Regarding premium tanks and refunds. Currently WG does not mind refunding a premium tank if you made a mistake and accidentally bought the wrong tank or something similar, as long as the tank has not been played.