Xephyr is the modern approach for easily running an X11 display server that targets a window of an existing X11/X.Org Server -- basically having nested X.Org Server capabilities. With Eric Anholt's work on integrating GLAMOR into the X.Org Server rather than being a standalone 2D-over-OpenGL acceleration library, he's extending it to allow for Xephyr 2D acceleration with GLAMOR. Xephyr normally isn't able to take advantage of 2D acceleration from the host server's DDX driver.
Eric's been working on the GLAMOR-inside-the-X-Server code for a while and this week he's posted the xephyr-glamor series for feedback by fellow X.Org developers. This patch-set converts GLAMOR to using libepoxy for hiding OpenGL vs. OpenGL ES 2.0 dispatch handling differences, adds a new "-glamor" option for running Xephyr with GLAMOR rendering, makes use of GLX swap events to reduce repaints, and allows Xephyr to initialize GLAMOR using OpenGL ES 2.0 with GLX, among other changes to Xephyr and GLAMOR.
This Xephyr feature will hopefully land with time for making the X.Org Server 1.16 release this summer.