Hey everyone, I have added documentation on how to essentially get Steam running in Funtoo using LXD. First, you will want to follow these instructions to get LXD running:
https://www.funtoo.org/LXD
Then, follow these instructions, which will get you to the point of setting up a multilib Gentoo container that can run glxgears. At that point, getting Steam running should be pretty straightforward:
https://www.funtoo.org/LXD/GPU_Acceleration
Please test it out and let me know how it works.