Fallout 4 is in development. That much is not debatable. However, the methods and such surrounding its creation is still the topic of much controversy. All we know is that Fallout 4 is definitely on the way. We're expecting that a trailer for the game will be shown at E3 in June, but that's just speculation. At worst, there will be no sign of the game and – at best – there will be a playable demo released to show-goers.
MrMattyPlays on Youtube is one of the foremost experts in Fallout speculation. He's actually made multiple suggestions that have turned out to be truth, so we're very interested to hear about his latest theory. This idea indicates that some of the assets from The Elder Scrolls V: Skyrim are going to be used in Fallout 4. He adds a disclaimer at multiple points in a discussion video that iterates this could be nothing. Bethesda Softworks might just be messing with the engine, but why would they?
You can see the video we're basing this off down below. It's worth the watch, so be sure to take a moment and check it out: