according to Storm, no more limited MM premium vehicles will be introduced into the game (save for extremely special cases). To that end, IS-5 (earlier, it was supposed to have limited MM) was changed to have full MM. This came with a penetration buff, from 175 to 221 of the 122mm D-25T gun.
Furthermore, the switch of crew’s specialization (radioman to driver for example) will not be cheap. The price was set to 600 gold and there is no credit option (it’s unclear whether this is the final version, but it seems so).