You have the right idea, but you're looking at the wrong angle.
All this is rounded:
Let's take roughly 1MM units sold of Wii U in NA.
800k users bought NSMBU.
150k bought the next-highest-selling title.
This tells us that around 80% of the market is only interested in Mario and/or NintendoLand, i.e. traditional Nintendo style franchises. Especially if other NIntendo-published titles still aren't higher than that 150k mark.
So, that's really the convertible market size we're looking at, roughly around 300k (users who didn't buy a wii u only for NSMBU, and factoring the software attach ratio for those that bought NSMBU + at least one other title).
If Nitnendo were able to convert 50% of this audience, that's 150k, which right now would put it as a top seller on the system. That's a really big conversion rate. The hope being that more hardware units by the time W101 launches + marketing efforts + Nintendo-published efforts to directly target NSMBU/Pikmin3/etc owners, would get them there.
That's not accounting for:
1) holiday factor
2) sales bump once M3D world launches
These factors could give it a longer tail. Which would be great. But it's better to be realistic about these things.
A note on marketing: look up what ROI means.
You don't just "spend" dollars unless you are expected to see a return.
NIntendo did the math on the ceiling they expect to sell, and are budgeting accordingly. W101 is just not their main 'investment' title, in which they have a large experiential budget. It's a return spend, so they will spend based on what they project to sell. Super standard practice here, gents. Sega may have spent a bum more, but their ROI was not there. Nintendo is more ROI focused. ITts really pretty formulaic. The Nintendo Direct is a low-cost and ownable way to specifically target their core consumer with their message, I imagine it exceed all their KPI's for it.
That said, even if W101 "only" hit 150k... it still would be right within the middle and better than some other Platinum titles sold in the US . Success!!
Your 150K in the end comes to a bit more than my 10% of install base but my point stands - will that be enough? I agree though that it's hard to know what Nintendo would consider success. I keep referring to this graph I saw some time ago, but can never find about the cuts each entity gets from a $60 title. IIRC that would leave Nintendo 30-40ish per title. So at 150K is 4.5 - 6 million. Minus expenses and there is their profit. Is that OK with Nintendo - who knows?
It also seems that they had predicted much better Wii U sales than what they have but development of the title started a long time ago.