Currently there's really no mention of when Fallout 4 will come out. People jokingly say it'll be out in about ten years, since that's how long it was between Fallout2 and Fallout3.
Improvements they should carry over:
-Sprinting. That was a godsend in Skyrim. I was so happy to see that sprinting function in the first gameplay trailer that I almost crapped myself. Fallout's wastelands are fun to explore, yes. The landscape is mostly too bumpy and craggy to properly use a motorcycle in such a large game. I want to at least be able to run places rather than fast traveling. Also, maybe I'd be able to keep ahead of those damned Deathclaws for the extra second I need to get through a door.
-I'd really love some kind of mount to ride. As Skyrim has shown, Bethesda is totally for making gravity-defying horses. Why aren't there any mutant horses or, hell, even a mountable Yao Gui or something? BEAR CAVALRY!
-Make sure to keep iron-sights. That was my favorite part of New Vegas. I used manual aiming down my iron sights more than I used V.A.T.S.
-I really liked Skyrim's skill system. It made it much easier to become a Jack-of-all-Trades, and allowed me to explore multiple skills at once. I can't really effectively become a Bare-Handed/Gun/Energy Weapons/Physical damage sponge all at the same time in Fallout. That much spread over so many different skills would leave me desperately lacking in other places...like LOCKPICK VVV
-I really like how lockpick in Skyrim just makes it easier to pick harder locks or gives you some good perks. I was able to open Master locks without ever putting in any skill points. Cost me a lot of lockpicks,but whatever. It always pissed me off in the Fallout games that if I wanted this amazing gun I'd have to actually sacrifice my GUNS skill to raise my LOCKPICK just to open a door to get it. "Okay, this lock is average, need Lockpick of 50." *Level up, dump all points into Lockpick...SKILL AT 49*
-A much longer and better thought out story. Skyrim's campaign was noticeably longer than either of the Fallout games, which could literally be knocked out within a day of playing from start to finish. Hell, if you remember where the vault your father is in is you can skip going to Megaton and Rivet City altogether and just go there. Beat the campaign in about ten hours, once. Seriously underleveled and it was tough, but beat it.