i have suggested the same thing but haven’t yet heard anything more about it. when zbrush 3 came out there a that was made for zcasting but has since been removed zbrush 3.1  so hope fully they will add it back in zbrush 4. actually this was mentioned briefly in this thread http://www.zbrushcentral.com/showthread.php?t=036912 around the time of siggraph back in 2006 a little ways down the page it talks about it. i cant wait to have that and the new lightbox and spotlight when zbrush 4 comes out , it will improve my workflow a whole alot since we will have reference transparency for proportion check, but along with that i hope we get multiple display support since it would make it easier to get to the right menu faster for those that have multiple displays they could use it and make the best of it as far as ui. that graphics card support to boost performance for those that have good video cards.
so please pixologic can you maybe think about adding this in a future update, even if it was something i would have to pay for as far as an update it would be nice to have and make life a whole lot easier…
at least consider it for future releases…