I don't care about CPU impact, I would very, very much like to have a "reverse" switch in Vegas. Is there some limitation that I'm not aware about which prevents this, or is it just on the "nobody wants it" list?
I think if you do a search through the forums you'll quickly discover that this is really on almost everyone's "i want it NOW" list. It's hard to imagine that there are technical reasons against it. Vegas can reverse audio while using the rate slider to scrub backwards. Audio Velocity envelopes of a sort are available in Sound Forge's Pitch Bend effect. Even ancient versions of Windows Sound Recorder have a reverse function.
My guess is that the main reason Vegas doesn't have this yet is because Sound Forge does, and Sonic Foundry wants to encourage people to buy Sound Forge.
Not true. When beta testing Vegas 4.0, this functionality was in there but was pulled before release due to complications with displaying reversed events in the trimmer, I believe.