Wouldn't a BW3 just have the same issue you mentioned with BW2? If you're going to have new plot elements that follow what happened in both games, including a version of Team Plasma, then new players are going to have the same issue of not getting the backstory. It'd arguably would actually be worse since you'd have two games worth of backstory that new players wouldn't have access to.Honestly be the easiest in terms of plot.
Either BW gets remakes and BW2 doesn't or BW2 gets a remake and BW doesn't and newbies don't quite get the backstory for BW2.
Meanwhile BW3 could just have new protags, plot elements and a another version of Team Plasma to focus on. Maybe now they just want to get rid of Pokemon completely.
If they were going for what would be the easiest in terms of plot, especially for new players, just doing the BW remake would be the route as you can tell that one's story without having to follow up on what comes next. It just wouldn't be the most satisfying way to do it as older players want those events at least acknowledged if not followed up on.