Matt,
Check out MixMeister. They have a simple, but eloquent interface for creating crossfades. I think this software has been mentioned before in other threads related to possible DJ features. What I personally am NOT expecting is auto beat matching, waveform presentation, volume curves, etc. Hey, it would be great, but I certainly understand what is involved with developing software for a wide audience.
I guess it would be cool to do all of this live for some people, but I'm not a live DJ. I do however create lots of mix CD's and when I host a "party" I'd like for the mix to be working so that I can relax and help with the drinkin'
Maybe you are responding to technical issues, I can't address those.
Unfortunately, the best way to do crossfading from a musical standpoint (not just creating dance mixes) is the way that Get it on CD, MixMeister, and Sonic Foundry approach it. Show the waveforms similar to Media Editor; move track B over track A and an editble crossfade is automatically created. If they don't overlap, there is no crossfade. Showing the waveforms let you immediately see the pattern of the music which allows you to match "beats" and other volume/musical shifts, visually and without needing a stop watch.
The hard part, as I see it, is to come up with a way to not do it the "best" way and yet still have a useful feature that won't drive everyone nuts while they are using it (Take a look at early versions of JAM, you'll know what I mean...)
If you want to go for the gold, here is an off-hand possible workflow.
I create a mix playlist. I've selected my songs in the order I think they will go; now it is time to mix. I go to the tools menu and select the new Mix Editor. (Or maybe you always start with the Mix Editor and the first question you are asked is what, if any, playlist you wish to mix). A new "window" pops up with a listing of my playlist at the bottom. At the top would be the waveforms that could be dragged around creating crossfades with editible volume curves. I could use the playlist to move the tracks around in the mix. I should also have access to my entire collection so I can add/delete easily...
This would be ideal for me. I don't know how many problems it would solve for others.