Re-rasterizing and blitting the whole screen on every change is clearly unacceptable, but there's a large gap between that and outright HW acceleration. Being smarter about redraws gets you a long way. I have used things like web browsers on unaccelerated X11, and it's been totally usable even on ARM.
But apart from educational purposes, why would you do that? Sure, the graphics driver is an ugly blob, but if you care that much about libre hardware/software, it would be odd buying an Raspberry Pi in the first place.
Granted, "for educational reasons" is a valid subject for the Pi. Get that old Abrash book out and let the OpenGL-spoiled kids feel the pain.
