I finally have a working demo using EGL and GLES under X11/Mesa (Kubuntu 12.04). I can run the most basic of ES1 and ES2 (as well as GL) tests under an EGL-provided context hosted by python-xlib (i.e. a raw X11 window). There's no guarantee that actual useful work could be done with it, but clearing the screen to red is working with all 3 apis on PyOpenGL head.
Unfortunately, the demo code is GPLv2 licensed, due to using sample code from python-xlib for the window setup. There's no real reason to use that other than that it was simple to get working. I could use any api that provides a raw X11 window ID AFAICS. I may revise to use wx or pygame in the future so that I could merge the test code back into the main PyOpenGL repository without adding all sorts of verbiage to the license file.
I'll need to get a working Raspberry Pi (all of my SD cards are toast thanks to disk corruption issues) to test on a "real" EGL/GLES environment once I'm confident that the basic operations are all there. I'm guessing that most of the "wrapped" functionality will need duplication, and I wouldn't be surprised if there are some missing extensions or entry points (likely due to the wrapper generator assigning them to GL instead of both GL and GLES APIs). At the very least, things such as the "shaders" convenience module won't be present in the GLES APIs.