Quark plans an OS X-only version for its next release.
Problem 1: The next version is a top-to-bottom rewrite. Quark traditionally has issued buggy initial releases (except for 5, which is really only 4.2 with a desperate bid for more money from the gullible). With a complete rewrite, the chances for this puppy working out of the box approach zero.
Problem 2: Don't look for this version until sometime after next June. Given Quark's usual pattern, this may mean 2004.
Problem 3: Quark is bleeding out. I receive offers to update some old 3.1 versions I own. But I'm putting my money on Indesign. How trendy.