To answer your question, the main question I would ask is "where would the benefits of the sale go" ?
I hope, benefit will go for the good of Wikipedia :), but it will be not monetary.
I plan this so: several wiki-users in Moscow will have a whip-round and order in printing office tee-shirts for themselves + a few as presents for admins (most active participants) and/or as prizes in contests. (If we shall agree upon it)
Also, I think, some people will want to print the same tee-shirts for themselves in other cities.
-- Cxion la plej helan, ajvol