I guess we'll just have to wait and see. Wait for about a decade until after the main Zelda after the BotW sequel has released and settled but whatever.
I agree that it will all depend on what kind of trajectory Nintendo takes the series in the future. If newer games are all offsprings of BotW like how MM to SS were Ocarina of Time-style games, or if they'll revert more towards the older gameplay style. I'm just saying, I'm not hammering down 15+ or 20+ million sales for every new entry in the series just yet.