As with any article that discusses why I think something won't happen, we should look at the reasons why it could.
On a surface level, it's great to hear Game Pass could come to Switch. The service has done wonders for Microsoft, and maybe it can do the same for Nintendo. The Switch doesn't have its own a la carte download service (yet?), and we could see two of the biggest names in gaming come together to provide something great for gamers.
The Switch is an attractive platform. It's growing and is big across all regions of the world, from North America to Europe and Japan. Microsoft has had a hard time penetrating some of these regions (namely Japan) and it could use the Switch as a vehicle for more revenues and accessibility.
Gamers would get an expanded library for a low-cost fee every month. Microsoft has a wealth of games it can offer Nintendo (not that the company actually needs this games, as its first-party titles are exploding left and right on the platform) via Game Pass.
One could also argue that EA brings its service to a competing platform with EA Access on Xbox One. The difference here is EA doesn't have hardware of its own, and doesn't have a streaming service and a huge webwork of services that are built specifically around wholly-owned hardware. Microsoft does, and its motivations are to bring its games to the widest audience as possible to promote engagement and spending.
The Microsoft-Nintendo partnership could see lots of changes and compromises to Game Pass to get it working on the Switch.
Game Pass on Switch would need to be a forked version that runs indies and other games optimized for the Switch, whereas every other major third-party game not optimized for the lower-end hardware would be streamed via Project xCloud.
This sounds like the future. Game streaming is ultra convenient and paves the way to a new kind of experience where users can simply integrate gaming into all facets of their life. Mobile gaming wouldn't be compromised to just smaller microtransaction-ridden freemium games. Instead, we'd get to play Gears of War 5 on our smartphones, and maybe on our Switches.
But there are so many roadblocks in the way for streaming right now that Project xCloud is kind of a pipedream that won't truly manifest until 2020 or thereabouts. The technology and online infrastructures are still very new, and there are lots of kinks to iron out namely latency issues. Plus the Switch's lackluster Wi-Fi chip isn't the best for online gaming, and it doesn't sport an LTE or 5G chip in its guts.
Even with this business plan, all of it sounds like a huge technical hurdle that Microsoft may not be ready for.
But could it be done? Maybe. Just about anything could be done with enough money thrown at it. The question is, how much do Microsoft and Nintendo want to potentially jeopardize on this bet?
Remember that Microsoft is a master of mitigating its risks. If it determines something isn't worth doing, like say investing heavily into singleplayer-only games, it simply won't. Instead, Microsoft likes to spread around its cash to multiple moving parts that generate revenue over time, like Game Pass, Mixer, Xbox LIVE--pretty much anything associated with the Xbox brand is built for long-term earnings rather than short-term sales.
Despite all of the things we've outlined here, Game Pass on Switch could happen. Things could change, and Microsoft and Nintendo may be willing to take potential losses and risks to make it happen. But everything we know about how the companies and services actually work tells us not to expect it to manifest.