Computers have gotten so powerful since Hexen2 came out, that simply displaying everything (world and entities) while no-clipping outside of the map isn't a problem. This is already enabled in the Darkplaces Quake1 source port, and it works great. I've done this before to glquake just by changing one line in the code.
This would turn noclip into a very useful map mode, in case you're having trouble finding an artifact buried somewhere. (as an alternative to constantly referring to walk-throughs for help on the exact location of an item.)