It's not going to happen if the Switch isn't a success.
The Nintendo Switch is in many ways a limitus test by third parties to see how well it performes in comparison to its competitors. Over the years, Nintendo has been performing unreliable by releasing mega hits such as the Wii, but also failing bombs such as GameCube and Wii U . It has behaved obnoxious in many regards and has been complacent in its attitude towards hardcore gamers and has constantly been persistent on its path to focus on being a family friendly company. Nothing wrong with that, but its a terrible strategy if you want to bring over third party games over to your console. If the hardcore gamers aren't there, then there is no reason for publishers to bat an eye towards that direction.
With all that said, and referring over to the limitus test, Nintendo has slowly been changing its ways. It has expanded its IP's to mobile, and has overall been more approachable in terms of listening to consumers, developers and publishers alike. Still, there's a ton of work ahead for Nintendo that it needs to adress and work on. Admitting its faults and adressing them accordingly is the first step towards that direction. It'll be interesting how it'll fare with the Switch, but there's not going to be an "unprecedented partnership" with anyone if the console isn't performing. We learned as much from Wii U.
So no, I don't think we're going to see GTA5 to the Switch for the forseeable future. However, if Nintendo keeps going the direction that it's going, then I'm sure we'll see more developers and publishers alike supporting them.