I think the renderer should be updated to a modern API. Not necessarily more fancy graphics (though that would be a plus), but rather just something that plays well with modern OSes. For example, with vanilla, on Vista x64, 2-d performance is horrible. I get massive lagging in the option menus, character stat screens, etc.
Well that's unfortunate. Is it only menus or does this occur while playing? What sort of trouble shooting have you tried? I have heard this is a problem with menu fonts, and in game messages. You could use ArxPak to edit the text message cfg file but I'm not entirely sure where you would need to start there. Hell, it might even be a ready file for d-load some place.
A cfg.ini change of forcegdi=1 to =0 could also be a possible fix.
I haven't had a chance to play the game on a x64 build yet, though I'm looking forward to it, and damned if I'll let it stop me!
[edit] Well here it is; unmodified Utext_English cfg file
http://www.megaupload.com/?d=C8ZM41FG
I'm eagerly looking forward to a zArx Fatalis in the mold of zDoom

It's unlikely to ever happen, at least not at that scale, but I can still look forward to such a thing.
It will happen I'm sure. It's a lot of work for pro bono, but there is always some crazy soul out there that will undertake the endeavor.