In Fallout NV you can side with Legion, NCR, House, Yes man... When they make Fallout 4 ( Assuming its after new vegas ) How do they know which one won in that game because there's different options...?

They'll likely just select one as canon like they did with fallout 2 were i to venture a guess.

Im guessing they wont refernce fonv at all except maybe to say there was a war over a dam and might talk about Mr houses technology hut wont say anything to who won or how its doing after the war.

I was hoping they'd let you select a saved game and when you play the next one they'd play it from what you did in nv... Probably not

Yea, if Obsidian was doing it there would be quite a few references & they would pick one of the endings as Canon and go with it. ...BUT, since Bethesda is working on F4, it's going be set on the East Coast & they will only, if at all, mention a War over the Dam. Bethesda doesn't like continuing plot-lines in their games, every game is a "re-creation" of the series.

If they don't want to continue games and want there future games to have no reference of previous games they'll run out of locations sooner or later... Why would nobody on the East Coast talk about that, that's like England taking over France and saying nobody in America will talk about it at all...

Consider their TES games...there is no references to prior titles in the series, minus a few little things, nothing major as with Fallout 1-2. They set every game 200years apart for that reason. There is an interview with Todd talking about TES and why they do it, if I can find it, I'll link it.