I don't really have an answer for that, I was thinking that myself, where can they take the series from here, but one thing I don't want is another game on same map and continuity. I am loving TotK, but I want to see a new world, and see what the devs can do with it.
As for games like older designs, I haven't played too many older games, so I won't mind those either, but if they do that, they should make that a separate series, like we have different Mario series. Keep one for BotW style games, and one for older styled games, but I don't think they will go that way. I think this is the kind of game they will keep making.