That's a total non-sequitor.

Because Mario and Pokémon are the past, Rabbids are the future.

I probably would have preferred just a Mario RPG game buttttt obviously if Ubisoft comes and pitches the idea and are going to fund and make the game (?) then they're going to want to boost one of their IPs through it. I think its more Ubisoft hoping that the Rabbids gain some more traction (unlikely).

That said, Nintendo wasn't going to make an Xcom like turn based Mario game any time soon so I appreciate this collab

originally I thought it sounded terrible, but it looked kind of like a good weird in the E3 footage thus far 

I bought Rabbids go Home (i think it was) for the Wii for my son and I thought it was a delightful game. As others have said they are similar to minions only more idiotic, chaotic and destructive. I personally think it will be a great combo and will add a great deal of levity to the game moreso then any other Ubi characters could have.

That is a major win for Ubisoft! 

I think this shows that: 

- Nintendo are going to be really open with more collaboration with their IPs to another one. 

- I heard that Ubisoft is making this game. Meaning that all of Nintendo forces are making other Nintendo games. 

- And with thise 2 points. Nintendo did say that they have a plan for more software output this time around. I think this idea is 1 of those plan. And I think it is a great thing to do. 

More exclusives with no Nintendo manpower used in the process. Nintendo can focus on something else entirely, while other companies use their IPs to make different games. Which is, honestly, the way I prefer Nintendo goes with third parties.

Either Nintendo is trying to show us all that they can work well with third parties or Ubisoft is expanding their portfolio of titles so they wouldn't be putting most of their eggs in a few baskets.

In exchange for some early Ubisoft support, they try to revitalize one of their old cash cows through Mario. Simple as that.

For the same reason Disney characters are in a Final Fantasy game.

Miyamoto said he has Rabbids figurines on his desk, wouldnt surprise me if Nintendo asked about using Rabbids specifically.