No, there is just no user base.
the reality is a massive # of people will buy Breath of the Wild when they get the system. So as the userbase grows over the next year or two, so do Breath of the Wild sales.
I think the critical reception of the game has sort of guranteed that Breath of the Wild may have a competitive chance of making it to like 10 million total. Bear in mind of the 13 million Wii U owners, we probably have to imagine at least a couple of million of them are going to pick up Breath of the Wild (and possibly bought a Wii U for that precise purpose originally, Zelda being mega delayed over the years).
We know that of the first batch of Switches (rumored to be like 2 million), the attach rate will probably be like 100% with Zelda. That alone puts like an automatic 4 million.
Lets say the system does so-so in the long run (i think it will do fairly well, but for the sake of argument), like 30 million in the hardware sold department- you have to imagine that Breath of the Wild is going to be one of those must have games for the system, sort of like a Mario Kart regularly, and will be purchased for like 1/4 of every Switch sold in the long run.
I think 10 million is very realistic.
Again, a lot has to do with critical reception. I'm kind of shocked the critics seem to like the game so much, I didn't anticipate it before, with it being such a departure from the past few installments of Zelda. But if most of the critics portray the game as potentially one of the best of all time- that's going to persuade an incrediblie amount of adpopters, and there already were plenty of people swayed before the critical response