Fallout 5 could be the best game if they simple enhancements and a renewed setting is made to the Fallout 4 version. Personally I'd really like better a companion system. The companions have been a huge part of Fallout for me but they've always been problematic in many ways.
I think it'd be great to have much more tactical control of their combat and general behavior. The other Big thing on my wishlist for a future Fallout game would a different setting. How about playing from the opposite side of the Great War.
A huge graphics overhaul is needed in the next version of the Fallout. It should be noted that the same kind of graphics are found in Fallout 4 as there were in Fallout 3. And Fallout 3 has been designed way back in 2008.