Hexagonal tiles will be replaced with squares.
Contrary to what was said before, the final decision is that there will be no old heroes from previous games.
Mapmakers most probably won't be permitted to change AI parameters or implementation. Players should trust Nival's AI programmers.
While the primary language is English, they have already begun translating the game into Russian. The English and Russian versions of the game itself, not only the demo, will be released simultaneously.
The magic system will not be tied to factions. Details will be revealed in November.
There will be Grail.
The demo version will be released well before the game.
The full list of information-worthy answers in this forum thread has been updated.