God bless you Tomoko for finding this gem.
Secure sources (nope, I will not disclose them because I am an a**hole and I want this to be posted only on TAP, so TRUST ME) tell that the mistery tank that Warsaw VIP ticket buyers will get is the…

leKpz M 41 90

Pictures (no pony): https://thearmoredpatrol.com/2016/02/02/lekpz-m-41-90-9-14-hd-model-pictures/
Tank info: https://thearmoredpatrol.com/2015/11/04/supertest-lekpz-m-41-90-mm-tier-7-light/