i was looking at the achievements to unlock promo cards and there is not one for unlocking eevee (promo 11). and then currently there are 2 others that are unattainable but i think you guys probably already know about those ones but just incase i mention. the achievement for mewtwo (promo 14) says coming soon. and then one other electabuzz (promo 2). that achievement requires one to collect all vending series cards and those arent out yet. so electabuzz(2) and mewtwo(14) have achievements but they are currently unable to be done. and then there is no achievement at all for eevee(11). and i only play gen1 so i was only looking at gen1 cards. there may be more unattainable cards outside gen1 but i dont know anything about that.
the promo eevee was supposed to be given out to the winner of a recent tournament on tcg one. but since it was never finished, no winner was actually decided. i actually wrote up ideas for how to unlock the unadded promo cards in another thread on the forums, which got some attention, and might hopefully give way for more ideas to add new promo cards