- Convince Adobe to release their suite on Linux! Push for/fund official Unity and Unreal Engine Linux versions Maybe they should just convince Microsoft to port over win32 and all the other APIs to linux? Whilst they're at it, they could also convince your most hated political figure to be more like your most loved political figure. With the convincing powers like these, Valve could just convince the world to no longer suffer from hunger.
The only incentives that work would be of the financial kind, however, paying for support is not sustainable. Console vendors can pay for first party or exclusive support from game devs because they are fairly sure this will increase revenue in the long term. Valve gains no more money if they incentivize developers to support Linux. I also don't really want for things to be supported exclusively on Linux unless if there are good technical reasons - I use Linux because of the freedom it provides me, I wouldn't advocate for people to be forced to use it. FWIW, Unity and Unreal run on linux, but a lot of developers elect to use windows-only Unity plugins. The developers don't care.
What Linux really needs is non-shit drivers and a mainstream desktop environment that takes into account input latency when developing it's window manager - Wayland on Gnome is really bad in this regard, yet Gnome is the target desktop environment for Steam OS (at least last time I checked). They should maybe make sure that their games run just as fast on Linux as they do on other platforms - currently this is not the case. I believe that solving these issues will be hard and may require a unilateral effort across various entities in the ecosystem - something which is incredibly hard to do, especially when it comes to Gnome. Then there's things like drivers - yes, performance wise Intel and Nvidia drivers might be OK, but they are not feature complete especially when it comes to power management. I don't believe there is a single problem that has to be fixed to make gaming on linux a massive success - there isn't even a shortlist of 10 incredulous tasks. It has to be a long-term effort and the open source community has to take part in it.