reQuiem is a custom OpenGL Quake engine for Windows and Linux. It's designed for maximum compatibility with all things Quake - past, present and future. It's fast, reliable, and easy to configure. In short: it fixes what was broken, improves what needed improving, and leaves the rest alone. It was developed by jdhack.
reQuiem already has some BSP-version-based fiddlery for supporting qtest maps (although only in debug builds?) so we'd have to be careful not to break that.
Cf.: https://www.quaddicted.com/tools/bsp2_format http://sourceforge.net/p/quakespasm/code/881/ http://sourceforge.net/p/quakespasm/code/892/
reQuiem already has some BSP-version-based fiddlery for supporting qtest maps (although only in debug builds?) so we'd have to be careful not to break that.