I don't think hey need to purchase new dev teams as much as they need to expand the ones they already have.
Namely, I think Game Freak could use quite the expansion for Pokemon Switch - which will be the first mainline, HD, console (or console-quality) game in the franchise and a huge leap from the 3DS.
I also think they can expand Retro Studios so that it doesn't take them 4-5 years to make 1 game like it's taking them now. Alongside working on Donkey Kong or whatever Nintendo franchise they're tasked with, they can make their own new IP as well, a more Western-oriented one at that.

I agree with a lot of what you said. They don't need to buy entire companies just the development teams that are responsible for 3rd party Nintendo exclusives and the rights to those franchises.

Although honestly I think it's more important for them to hire fresh new talent and make studios out of those developers, especially in Europe. Nintendo really needs Europe focused games to try and gain some leeway in that area.

Somehow i doubt Mario strikers would every take off like fifa : P "
but could work!

It is something they may consider doing as they note how the game flow from them is with only one system. They are probably still testing the waters first before such a step

Nintendo is OK like they are curently, espacily now when they have only one platform to suport,
saying that, they would definitely need to keep founding or investing in second and 3rd party exclusives like we saw with Bayonetta 2/3 or Fatal Frame V.

The funny thing is that Nintendo has been hiring. They haven’t really let go of people from what I’ve been reading. Even during the struggles of the 3DS/Wii U, Iwata took two pay cuts to keep staff and prevent harm to the company’s morale. They were hiring then.

Now that they unified the development for their handheld and console division, I don't really think this is necessary. They've basically put out a fairly major release each month. More than that would be stepping on their own toes, and would also make the environment less hospitable for third party devs.

Their current size along with some supplements from third parties utilizing their IPS (Pokken/Rabbids) and publishing the odd exclusive (Bayonetta 3) seems to be working fine.

You just need enough microtransactions.

Playtonic. They have the veteran experience, but they need Nintendo’s QA and I’m not sure they’ll survive on their own.

Ah, so essentially we're past the direct colonization phase, and have moved onto the neo-colonization phase, where they don't officially own the smaller developers and publishers, but they exert great influence on them.