In the latest edition of Suellen and Mark Adams' column at MacGaming.com, the two developers from Westlake Interactive explain why there won't be a Mac port of UnrealED. Even though the editor was recently rewritten in the more Mac-friendly C++ language, it is still far too Windows reliant to be feasible. Here's an excerpt that explains this:

With the advent of the C++ version, many people just assumed we would now port it. After all, those technical reasons were all about Visual Basic, right? C++ is a Mac-friendly language, right? Unfortunately, Tim Sweeney's observations about the new editor's platform-specificity were correct -- UnEdit, even in its C++ version, is so full of Windows-specific calls, that it is still a total rewrite for the Mac. It is not a recompile, or just some tweaks. It is what we would call completely non-trivial.

It is non-trivial work-wise, time-wise and money-wise. Our estimates are that the editor would take as long to port as Unreal itself took. Since it would take roughly the same amount of time to port the editor, it would also take roughly the same amount of money. The original Mac Unreal has never made back the advances paid to Westlake by the publisher. Since the PC editor was included for free with the PC game, a Mac publisher couldn't put the editor in a box and sell it in stores. This means about the only possible way to generate enough money to pay for the port would be to release it as shareware. By our calculations, even if over half of all Mac Unreal owners paid a standard shareware fee for Mac UnEdit, it would still just barely pay for the work.