Layton was always niche thing and it needs to play different strategy. You know, how you would do it? You want to spice up things, so new character is needed. But Layton is incredibly smart and experienced, so he would overshadow any new character. Make him sort of mentor, aiding once in a while? It doesn't make any sense for him to be only observer, Phoenix Wright could pull it out, but with incredible writing. The easiest way to flesh out new character is to remove old for a while. With time, new character won't be seen as ,,mini-Layton" anymore, but strong personality on its own, not overshadowed by Layton. It will allow for better plot and games in future.