I've been a strong advocate of breaking steam's monopoly over the years but, in reality, the more time passes, the harder it becomes to do so.
The competing platforms should have happened before 2010 when steam was just a DRM content delivery platform; through the years, it has become a social media platform, a workshop, a gambling platform, a game startup incubator, and generally an easy way to make money. Gamers and developers alike are now deeply rooted in steam, and migrating to a new platform might prove cumbersome. People by default do not like change. It's still feasible though but the new platform has to be very lucrative for both gamers and developers to warrant all the hassle of moving.
If a new platform offers the same services/games as steam in addition to some REAL customer service, then I expect steam to lose at least quarter to half of its market share in a year, and you could see an exodus of gamers and devs. In this case, even a new IP/game from Valve won't save them.
What Valve might, and probably will do is add new features to steam to prevent further market erosion and lure gamers/devs back. I highly doubt they will think of a new game to save the platform.
There is always a tried-and-tested way to make them change their minds (and @Sprony will back me up on this one ): vote/protest with your wallet; let them feel the heat.
I would have to disagree with you on the single player experience. Some games from the 90s are still being played today; the magic "ingredient": mods.
You make a great game, make it moddable with a proper SDK, sit back and watch it live long past its expected shelf life.
Case in point, Half-Life itself:
Awesome, ground-breaking single player, coupled with a decent multiplayer component and a myriad of free mods is keeping the game alive til now.
The problem in games started when "the suits" from upstairs started to have the last word in games over the creative people.
The shitty concepts of paid DLCs, early-access, and micro-transactions started to creep in, and this has become the standard way to keep your players hooked.
As for VR, it's a nice concept but I don't see it as a crucial necessity in today's gaming. You can well game and live without it, hence the very slow adoption rate.
I honestly don't see it becoming mainstream in the next 5-10 years; after that, who knows, maybe porn VR will become the norm and force the adoption of VR