There is two kind of hybrid graphics: MUX-ed and MUX-less (
read carefully here). vgaswitcheroo may switch GPU only on MUX-ed laptop (and only if this laptop is supported by vgaswitcheroo). On MUX-less laptop vgaswitcheroo can only turn off second GPU, nothing more. All laptops propduced in latest two years is MUX-less. Proprietary driver support only MUX-less laptopts. vgaswitcheroo is not available when you use propritary driver because proprietary driver have own internal solution for hybrid graphics.
Offloading rendering with FOSS drivers (read it: proper support of laptops with MUX-less hybrid graphics in FOSS driver) probably will be available next year.