Due to the size of the hype with the announcement and the fact it was first mentioned on the end of a trailer for B/W2 i think it has to be a new game. Anything else would be posted elsewhere i think the game will one of 3 things but 2 are unlikely
A R/S/E remake would be my personal preference but due to the fact almost all the pokemon can be caught in later games and the poor reception of the games and the low sales would all suggest that this wont be it. Also why not release it to coincide with the Japanese 10 year anniversary.
It seems to soon for a new generation - there was about 2 years between E and D/P and likewise with Pt and B/W. It will barely be a year between B/W2 and whatever the new Gen games would be.
What seems to me to be the most likely but personally out of the 3 my least favourite option is a new Spin off game for the Wii U
But i guess we will all find out in the morning and see who if anyone was right.
"over the laws of light, over the moon by midnight"