according to an interview for a Polish website (from an interview with developers at Gamescom), Polish tanks are coming next year to World of Tanks with the first Polish tank being the 20mm version of the TKS tankette that will come in early 2016.
That's the good news (for Polish players anyway). The bad news is - premium tanks only, no regular branch is planned. So far two or three premium Polish tanks are planned for next year. It is currently not known what crews will they have, it's possible they will form some sort of "Polish minitree" with premium tanks only - or they will be a part of the Soviet tree the way the Turán appeared in the German tree. We'll just have to see.