For open-source graphics drivers materializing last year and earlier in the year was the PRIME support in conjunction with DMA-BUF for buffer sharing between drivers/hardware. Released last month was then a new NVIDIA binary Linux graphics driver that supports NVIDIA Optimus and RandR 1.4 at long last. On the AMD side for hybrid graphics, the Catalyst driver has its own way of handling Intel+AMD mixed configurations.
Discussed earlier today during the virtual Ubuntu Developer Summit was a session on eveloping a hybrid graphics support strategy planning, something that's been talked about at many UDS events going back years.
The X.Org Server and Linux kernel found already within Ubuntu 13.10 has the necessary patches for basic hybrid graphics support, there's now support within Lightdm, and the GNOME Settings Daemon still needs to learn about the RandR providers support. Another item still left to do is updating the Ubuntu xrandr packaging to version 1.4.0.
Some other upstream happenings include synchronization and fencing support for DMA-BUF likely coming in the Linux 3.11 kernel and TTM and other improvements coming to the Linux 3.12 kernel. There's also some other outstanding X.Org server patches left for upstreaming.
While the X.Org support is there for Hybrid Graphics, their own Mir Display Server doesn't yet support hybrid graphics or multiple GPUs and it likely will not do so for quite some time.
Long story short, largely thanks to the upstream Linux developers and the work by NVIDIA's Unix driver team, hybrid graphics support for Linux is slowly but surely coming together. For Ubuntu 13.10 it appears the support will be in mostly good standing aside from some kinks to work out and waiting on Mir support.