Miscellaneous:

Larger Stash - The stash size is to be increased drastically, it's believed up to twice the size of the current one.

Game Interface - The game interface will undergo a few minor changes but none are expected to effect gameplay.

Changes to Current Characters - At this time there is no planned changes occuring to any of the characters already included in the game. Possibly in a patch but the game is fairly balanced as it is.

Arenas and Guild Halls - At first these were to be included in the original Diablo II and with the announcement of the Expansion Pack many thought they would be a for sure. Blizzard actually decided against this because they realized both types offer a completely new and possibly unwanted type of gameplay. It would also need so many new features that would alone take up to a year to develop Blizzard said the features would actually need their own expansion pack just for that.

X-Pack Beta - It's not expected to have a public beta but a few elite people may be chosen to test the game out.

End Game Countdown - With the expansion the countdown timer that you see in Act IV is very likely to be removed.

Gems - At this time no new gems are slated to be added

End Game Countdown - With the expansion the countdown timer that you see in Act IV is very likely to be removed.

Upcoming Games:

Starcraft II - "We're not doing SC2 and that's because of various reasons, the technology we wanted wasn't there, the advancements, they just weren't around". (Joe Morrissey, Blizzard North)

Diablo III - "We have no idea, we have no concept, we haven't even begun to think about it. We are 100 percent focused on the Expansion Pack." (Joe Morrissey, Blizzard North)