it would be great if you had a tool that would allow you to record in real-time (with no click or other time reference), then let you to build a tempo / time signature map in reference to what you played live.
all you'd need to do is designate markers where you want each bar to start. or each quarter note, etc...
then, your song will follow YOUR feel. not the other way around. plus you can then sequence other midi or audio parts to lock in with your new tempo map and apply quantization to based on the tempo track, etc...
also, it would be cool if you could then do the reverse and quantize your audio to fit your tempo map. unlimited possibilites...
another common sense feature the big boys never implemented...