But that would have to take place in the XYORAS timeline and thus would be a BW remake instead of the 3rd installment of BW.
That being said I wouldn't mind Bronius, Ryoku, Gorm and Giallo getting their own story arcs as they were practically filler material in BW and never appered in BW2. Could be about Nationalism vs Imported Culture of Kalos.
Also pokestars studios is in serous danger of closing ever since Ruin Tech Town CinimaWorks took the industery by storm and part of the post game content has you competing against the rival company(Which would make the earnings actually mean something instead of just bragging rights). Most importantly, they need to bring back intralink mini games instead of the bad mini games from super training and amine.
Lastly Black city/White forest should have a true mystery dungeon mode where all your pokemon are reset to ~lv10 and movepools reset(some lame excuse like rental pokemon only will do). Has infinite floors, a boss trainer for every set of 3~4 floors that unlocks the next set of 3~4 floors with no breaks inbetween. Nurses should still be there and there are random trainers that will teach you randomised moves to one of your pokemon after you defeat them. Doing this challange will give you a woop ton of Battle points comparable to the battle subway.