Never used Ableton, but I've been dabbling in Reaper[0]. I can't make a full switch yet, but am hoping to be able to at some point in time. From the little I've seen it isn't missing anything major.
Final Cut Pro is another story, but I really don't use it very often anymore, and I'm well-versed enough in Adobe Premier that I could probably drop it.
I'm not holding my breath either, but I do dream of a world where most software is OS-independent. I guess we're closer now than we have been for a while.
EDIT: I just remembered that Reaper is Win/Mac. I hear it runs under Wine, but I'd be worried about latency there. Alas, we are captive to our tools.
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[0] - http://reaper.fm/