We love all these free new tanks, and we will love and pay for the DLC's as they come along. But there is a problem, common to all "collecting" games following the Panini sticker model. As the number of tank types increase, so do the junk yard and excavation sites clutter up with stuff you have already got...
The game becomes boring, until that missing Goliath or King Tiger turns up. It's going to get worse with each new tank added to the game. There is a balance between grind and easy progress, and the grind will only increase, for anyone that does not want to fix or dig up endless T34's, Stugs and M5's and is trying for that missing museum exhibit.
It happens with the Panini stickers too, with each pack purchased being less cost effective for the buyer. With the stickers it's part of the business model. They just want you to keep buying packs. But with Panini, when you have lost all patience, at least you can send off for the missing stickers.
Perhaps something like this might work, an occasional email offering to sell you a tank wreck of one of the rarer tanks. Of course it would be expensive... but then it is rare!