You've got a few years more at the minimum. What Bethesda needs to do is just hand the entire project over to Obsidian and start working on Elder Scrolls VI: Valenwood.
They have to release fallout 4 special edition, then release it to the switch. Followed by a special survival mode and then just continuous releases until they get bored.
They should call it fallout 5 fall in and make it like a national selection service thing were you must fight for your own country but you turn rebel and recruit your rebel fighters and fight against your own goverment after the nuclear fallout
Bethesda takes their time with games. There was a 5 year wait between Oblivion and Skyrim. Fallout 3 & Fallout 4 had a similar waiting period, with Obsidian making NV in between. Patience is a virtue.