Well, you can't stand out by just following what big companies are capable to offer better.
True, but thats not necessarily the main reason I mention the idea. There are doubts about whether or not SteamOS and linux gaming in general will get anywhere compared to mainstream windows gaming, if it doesn't gain enough momentum hardware manufacturer's may lose interest and let their drivers lapse again. Getting a boost of double the library would inject a much needed sense of progress and legitimacy. In other words rather than dividing the market further, we could pool our resources to try and increase the odds of generating a successful linux market.
Anyway, having an ItchOS doesn't mean that the main app couldn't work into steam as non-steam app.
And vice versa. I'm not saying don't make ItchOS, only that we have the Itch.io App right now and building roads into SteamOS could prove beneficial for both parties. I think there's a strong argument for ItchOS, not just because the linux library is larger on Itch, but because it could provide a DRM free alternative to SteamOS, be more developer accessible, add some useful features like USB live sessions out of the box, have lower spec targets and builds, and include accessibility for the disabled beyond what Steam is capable or willing to offer.