I was including Switch + Wii U together for my BotW prediction. When I checked the reported numbers last (Mar. 31, 2018) Zelda was only about 0.5m behind Mario. So if it sells 6000 per week for 6 years that is 6000*52*6 = 1.872m. That is more than enough to catch Mario and it isn't counting increased sales from holidays either.
Mario will be more advantaged for Christmas against Zelda, exactely for the same reason which makes Switch to be advantaged against PS4 :
Mario has more success to younger players, Zelda touches more adults. If I buy a Switch, I will buy Zelda for sure as my first game, but not Mario. I know a few other like me around 35 years old who wants this Zelda so much but not Mario. Most of the adults don't care about the period of the year to buy a video game. But younger with no money during the year have to wait Christmas.
Current PB on Secret of Mana remake : 2h27 (2nd)
Strongest worldwide achievement on TGM : 1st European S13 rank
Fastest TGM3 MASTER in Europe : rank Master V in 5min10
Western record on TGM3 EASY : 1484
Current PB on Power Ranger (Game Gear) : 10min06 (World Record)
Non-geek activity : ThermalHungary