Source: Yuri Pasholok - MT-25
Translated (and redacted by): Silentstalker
Well, so much for Yuri Pasholok's article. The reason the T-50-2 is going to be replaced is that the T-50-2 (and the T-50 when it comes to that) doesn't behave as the real life original tank did. From the other threads on the RU forum, it's possible it will have various 76mm guns, including possibly the S-31. The engine mentioned for it is the KV V-2K (600hp), which is not bad for 25 tons. The armor was supposed to be the same as the T-50 (as far as I can tell at least).
Other pictures (from the Russian archive):