You're up to write a bugreport to steam to support hybrid-GPU systems. Its just that for some users, with the latest steam update (client, not this package) it will not work anymore.
BTW you can also edit:
~/.local/share/Steam//userdata/*/config/localconfig.vdf and add the every game
"LaunchOptions" "DRI_PRIME=1 %command%"
(or optirun, primusrun, whatever nvidia supports). But other than this we can not do much about it.