Jk2 has rather crude and ugly looking fixed shadows and lighting while Quake3 maps are able to have much smoother, realistic, better (shadow, lighting) maps because of improved map compilers. Would it not be possible to alter a better map compiler to produce JK2 map formats, while also adjusting the needed constants and variables in the JK2MV port to allow higher quality Shadow and lighting maps ?
I know that it is possible to get jk2 maps into ioquake3 rather fast by ignoring (not correcting) the colors, shadow maps, and more... which makes me believe that the team behind JK2MV should be able to do all of that.
However, The bulk of the work might be in the Map decompiler if one would want to rebuild the original Multiplayer maps with much higher quality static shadows and lighting.