Looks like there are four spots left to be filled, at 77, 78, 97, and 98. I think it's safe to assume at this point that they are all to be part of the Legendary Treasures blisters. The Battle Carnival mew is confirmed to be one of them! leaving three others open. Personally, I think they are going to be the Movie reprint of the Red Genesect, as well as the Shaymin and Victini that were given out with the purchase of the Mewtwo vs Genesect deck, since the cards from that deck were translated into Legendary Treasures, and they made a big enough deal about that to include Mewtwo and Genesect on the booster packs. Additionally, these two cards fall into the spectrum where they would be nice for beginners to use in decks and definitely have some use, but might be negligible in serious tournament play.
For record, here are the four cards that I think we're getting. Remember Mew is confirmed, and the Genesect with the blue background is the one I'm talking about (we already have the other one).
http://bulbapedia.bulbagarden.net/wiki/Mew_(BW-P_Promo_220)
http://bulbapedia.bulbagarden.net/wiki/Genesect_(BW-P_Promo_232)
http://bulbapedia.bulbagarden.net/wiki/Shaymin_(BW-P_Promo_233)
http://bulbapedia.bulbagarden.net/wiki/Victini_(BW-P_Promo_234)
For record, here are the four cards that I think we're getting. Remember Mew is confirmed, and the Genesect with the blue background is the one I'm talking about (we already have the other one).
http://bulbapedia.bulbagarden.net/wiki/Mew_(BW-P_Promo_220)
http://bulbapedia.bulbagarden.net/wiki/Genesect_(BW-P_Promo_232)
http://bulbapedia.bulbagarden.net/wiki/Shaymin_(BW-P_Promo_233)
http://bulbapedia.bulbagarden.net/wiki/Victini_(BW-P_Promo_234)