It's already possible to partition GPUs to share them across multiple VMs. Intel's got modified versions of Xen and KVM to support this for Haswell and later IGPs, and AMD and NVidia both have proprietary solutions.
Furthermore, this has nothing to do with rendering APIs; it's all in the driver and hypervisor.
Yes, running the VM would be silly, but machine learning etc. is awesome. We get acces and time sharing across resources much easier (at all) now. At Graphistry, we are using AWS G2 instances for previously impossibly big interactive data visualizations and streaming into stock browsers. It's pretty ridiculously cool :) Always happy to chat about GPU clouds and related fun things.
Furthermore, this has nothing to do with rendering APIs; it's all in the driver and hypervisor.