Well 3D Mario + Bowser's Fury will hit it, BD/SP already did, PLA obviously will, Mario Party Superstars obviously will, Luigi's Mansion 3 already did, Kirby might, BotW2, Splatoon 3 will, gotta imagine there will be a 2D Mario on Switch at some point which obviously will, then there's the questions of will another 3D Mario and/or MK9 come out on Switch which would add two games to the list if they did, they should be at least one more Pokemon on Switch which will, if the next rumored DK game is something fresh and special that has a longshot chance to do it.
So there's still plenty of 10 million sellers coming to the Switch to add to the current number.