Nintendo has games and marketshare, their business won't be even be touched by the Steam Deck... If it were to sell at least half as much, maybe they would talk about it in a meeting
Counter-argument (just for the sake of it):
Due to increasing financial pressures, consumers will become more sensitive to their purchases and the practices of the Big Three over the next few years. This, while at the same time most companies are feeling increasing pressure to 'adapt' to the market and squeezing revenue out of their (increasingly cash strapped) consumers.
As a result, there will be a return to 'alternative means' of procuring software/entertainment. Emulation, piracy.
Steamdeck represents the perfect nexus between consumer value (cost/perf, access to STEAM, 'PC' open platform/Linux) and 'options' (emulation, piracy). In particular if Valve doubles down on long term support of the hardware (new releases), and software (Proton, SteamOS).
Nintendo could begin to feel pressure here. After all, why pay Nintendo prices for their software and hardware if you could pay a bit more (or just as much? we'll see..) for a Steamdeck and have access to everything + 'free' Nintendo games on their current platform (Switch), and future ones due to piracy/emulation?
Even the initial conversation for something like Steamdeck 2 for the average person could be pretty simple.
"Why did you buy that handheld thing over a Switch(2)?"
"I wanted to play God of War Ragnarok plus Stellaris. Besides, it doesn't really matter. With a little work, I have my entire Switch game library on here and they're already working on a Switch 2 emulator."
"Wow, is it hard to do all this?"
"Not really. Let me show you a few youtube videos and Github links."
Regardless of whatever one may feel about piracy, it is inarguable that it will force companies to hesitate before bending consumers over the barrel. I predict we will soon see a dramatic resurgence of the practice. Steamdeck is uniquely positioned to benefit.