In addition to platform-specific hacks being contrary to the CS design philosophy, they\'d also probably be a nightmare to maintain.
As far as I know, the main problem is related to Apple\'s \"interesting\" approach to texture management. Because they\'ve done things ... \"differently\" (for good reason, mostly), the standard way to do lightmapping in CS comes out horribly slow. One hack has already been implemented, and that got the framerates up to something usable for most development purposes (although probably not for planeshift...)
If it is possible to abstract the way CS manages textures, making a \"platform-specific hack\" might be feasible (since upgrading to Panther costs $$, and I don\'t have $$, and I\'d like to be able to play Planeshift some day.)
That said, it\'s been a while since I took a look at why Crystalspace is a bit slow for me (on my Mac)- at one point, it seemed to speed up ridiculously, but then it quickly went back to normal (during a weird sequence of buggy system updates)
I\'m pretty sure the PlaneShift team wants a Mac version, more so than Valve. In addition, the Crystalspace team also wants good performance on all platforms. It might take a while, but it will happen.