This is a very myoptic view of current and future trends. Why would console makers want to consolidate their audiences? It does not benefit console makers or consumers. The only entities this would benefit are third party developers.
The last thing this industry need is for third party developers to have too much influence. They have been responsible for most of the worst anti consumer strategies/tactics to date. Microtransaction in full price games, "time-exclusives" releases, barebone games with gaas model that inflate games prices beyond 100 dollars, pay to win, lootboxes, etc.
Making things easier and more sustainable for people who make games (whether larger 3rd party studios, internal studios, or indies) is optimal for consumers. More high quality games, cheaper games, games delivered in a reasonable timeframe, more players to play with - these are things that favor me as a consumer. MS releasing Xbox games on PC or allowing crossplay with Switch is "bad" for Xbox brand but "good" for their total software sales, good for the game publisher, and good for me as a consumer by giving me more choice, why would I ever lament that move?
There is nothing to be gained for consumers to put all of their eggs in a single console manufacturer basket. They are boxes that deliver content, whomever makes the best box with the best services and value should get the most consumer attention. That has varied from generation to generation because console manufacturers will invariably choose to exploit their market position to maximize profit, as they are publicly traded companies and their shareholders demand that they do so.
Sony, MS, and Nintendo have all made anti-consumer moves in the past (including, but not limited to, pricy DLC, online paywalled gardens, region locking, blocking crossplay, blocking voice chat, deactivating servers prematurely, lack of BC, limited edition DLC by way of amiibo, pricy peripherals, BUYING those time exclusives or marketing exclusives for games that don't genuinely need funding, full priced HD rereleases, high HW prices due to unwanted features, removing wanted features in HW revisions, proprietary physical and optical media, proprietary storage, locking out third party peripherals and storage, forcing devs to include new content in ports, forcing simultaneous releases, limiting or charging for content updates that devs want to give out for free, etc).
They are not the "good guys" with 3rd parties being the "bad guys". Everyone is just trying to make money. Allowing software purchases to be more universal and shared is better for everyone
except Sony/MS/Nintendo, how are those 3 companies elevated above the entire rest of the industry?