I don't think this is likely. There is a convincible future where Nintendo publishes more and more games outside of their hardware platforms, so Valve needs to keep good business relations with Nintendo.
This future seems very unlikely. Nintendo has published like 1 phone game? They are very much a fan of their garden.
It course I would love to see this. I think Nintendo makes some very good games but have no interest in having specific physical hardware do end up not playing them.
There current lineup of mobile games are Mario Kart Tour, Animal Crossing Pocket Camp, Fire Emblem Heroes, Super Mario Run, and Pikmin Bloom. These have brought in over $1B in revenue, mostly from Fire Emblem.
Additionally, Nintendo is heavily involved in The Pokémon Company, so they saw the closed doors numbers of Pokemon Go.
I don't think it's crazy to think Nintendo will have a major presence outside of its own hardware in the future. Nintendo as a company always feels about two bad console cycles away from ruin. This feels doubly true with them putting handheld and console gaming into the same basket with Switch.
I also don't think it's crazy for Nintendo to decide that they can sell more games if they sell them on other platforms. In many ways the whole concept of a console exclusive is legacy thinking when the consoles had major architectural differences and porting was a major process.
