I think Nintendo could offer different services on different platforms. Nintendo might have exclusives on future Switch successors, but maybe offer certain evergreen games and retro games on other hardware platforms. Wii remakes might do well on VR platforms. Though Nintendo could just stay the course and as long as people keep buying their stuff then they have no problem.
Though I think Nintendo is a lot more forward thinking then people give them credit for.
Microsoft can always offer classic games on their service too. There are no shortage of classic games they just bought. Activision has been around since the Atari days. Their whole existence was started as an insurgency of unlicensed 3rd party games on the Atari Platform. They also probably triggered the 80s gaming crash.
There is no doubt all the companies will have less diversity of content moving forward. Some studios are going to become specific game franchise houses. Though they might revive some dead franchises. Blizzard hasn't made a new RTS Warcraft game since 2002. Warcraft became an MMO series. Microsoft however has continued to make Age of Empire games. Simple solution: have the age of Empire team make a new Warcraft RTS game. Flip that around and maybe there will be an official Starcraft MMO game.
Sony looks bad at the moment, but that is only because of the comparison. I have a ps4 for a reason over an Xbox One. The exclusive content on ps4 was just something I preferred. Though 360 was more appealing the previous generation. Sony has a good stable of internal studios, and good third party support. Activision Blizzard was just one large studio. There are still plenty of multi-billion dollar studios like EA, Take Two, Ubisoft, Square Enix, Capcom, Sega, Bandai Namco, Roblox, CD Project, and Konami.