The final fix was just committed moving the glXMakeCurrent call to the _render() function (and, thus, the _coreloop thread). I've tested it to work on rage128, radeon, and nvidia (TNT2) cards.
Most notably we're still missing the event callback for changing the window's _width and _height when it's resized and the size __set__ code for changing the windows size from within Python. We could also use several more attributes and methods for, ie, checking and setting wether a window is minimized, to bring it to the top, to change it's title, etc.
But that's just Window()-dressing, if you'll excuse the pun. The important thing is that we once again have a PySoy which renders.