I don't understand all these people somehow thinking that Nintendo will buy some Ubisoft stake.
What does Ubisoft bring to Nintendo?
-Some ports of needed 3rd party franchises
-Perhaps some creative projects like Rayman/ZombiU that work for a while but then get ported to other consoles anyway.
Either way, having Ubisoft on board porting everything doesn't really increase the appeal of their hardware to a significant degree compared to the competition, and if Ubisoft continues to make best sellers this really only benefits the hardware of Sony and MS more than it could ever benefit Nintendo.
Now we can think darker.
What can Ubisoft falling to Vivendi mean for Nintendo?
-In the worst
case scenario lets assume that Ubisoft is totally gutted, a major talent exodus occurs and the studio stops finding commercial success due to poor game quality. This means that Nintendo, whose main software selling point relies on their first party doesn't lose that big of a hit, and any potential licensing fees are dwarfed by what those games give to Sony and MS. It also means that in comparison, the competitor platforms manage to look worse due to this total breakdown in quality and how they sell by the strength of their 3rd parties. TLDR: All of them lose in this case but the others manage to lose "more".
Now of course this is talking only about the worse case where Ubisoft just gets totally shelled, but either way, Nintendo doesn't not gain much by risking this kind of move, nor do they stand to lose a great deal if they choose to do nothing. So they do nothing.
If ANY of the major 3 were to buy out a stake, it would be Sony and Microsoft but only if they could get exclusive rights to some key franchises which would cost a ton of capital and probably at that point is pretty much a takeover therein of itself. Anything less and your other major competitor still gets all the same games you do so what's the point?
The inverse of situation is largely the same, if both choose to do nothing and the worst case scenario still happens, you lose some but the other guy loses near an exact amount in terms of # of games and their quality. All in all, it either requires some serious muscle power in terms of $$ or you both stand to lose and there's no reason to really take a risk on that.
If it would have benefited any of the major 3 they would have already done it.