Far Cry 4 Creative Director Alex Hutchinson gave quite a lot of new information on the game, and on what he would have liked to put in it but wasn't to be, during a podcast on Game Informer, aptly summarized by NeoGAF user sjay1994.

• The map size is relatively the same square footage of Far Cry 3's rook island, however due to the mountainous regions, the map is far more dense than that of FC3.
• The team behind Far Cry views the games as more of a series than a franchise, as it doesn't need to worry about narrative baggage. This factors in to what Dean Evans and his team are doing. It might not be Blood Dragon 2, but rather something unexpected
• When asked about temperature, Hutchinson said he would love to make an extreme Far Cry game akin to what the modding community might come up with. His ideas were you get hypothermia when in cold water, you contract diseases when certain animals bite you, permadeath, etc. However, the main game doesn't have anything to do with these hardcore options, the team might consider making a mode for it if there is interest.
• No sharks in FC4, but there are demon fish and honey badgers.
• Thin air is a factor in some mountainous areas. You need to have oxygen in these areas, and you do not have much of it.
• There is an avalanche setpiece in the game, but players can not trigger them freely.
• When a player buys the PS4/PS3 version of FC4, they will get around 10 tickets called "Keys to Kyrat",that you can give to friends. They will be able to download a limited version of FC4 that has all the co op content and everything but the single player content. They will only be able to play the limited version if you are playing the main version of FC4. Hutchinson is not sure, but Sony might implement a time box.
• There's no split-screen co-op.
• There is a competitive multiplayer mode in FC4. No details were given. The team views FC3's multiplayer as unsuccessful, but are using lessons they learned to hopefully build a fanbase with FC4's mp.
• You will unlock the wingsuit pretty early into the game.
• In some of the games cinematics, players can interrupt them with actions, however they player will not have a prompt to do so. These will be hidden. This was made to address Far Cry 3's quick time event-driven boss fights. Also, it sounds like there are no QTE's in FC4.
• You can throw grenades through enemy car windows while you are driving, and drive away.
• Fire still spreads in Far Cry 4  like in previous games of the series.
• Hutchinson had lots of ideas to use dung as a weapon, like using it to coat arrows to make poison, but the team denied the possibility.
• You can turn off the HUD, and each element of the UI, like XP feedback, etc. It's designed with the next gen consoles sharing features in mind.
• There are multiple endings, but they are less clear than in Far Cry 3, so there's no press LT for good ending, RT for bad ending.
• You can pick sides with the different factions. This will effect relationships with different characters and can effect the endings.
• You can reset outposts, but the team is giving a narrative reason for it.

The hint to a possible successor to Blood Dragon definitely has me excited, considering how much I enjoyed it. Hopefully this one will be just as wacky. Probably the best part of it all is the lack of quick time events. They seriously spoiled boss fights in Far Cry 3 for me.