Pretty much anything that Joni Mitchell would ever play live. Her fear of flying has stopped her travelling for years, and her recent ill-health probably means no more live performances. 😐
Seeing the original Genesis line-up play Supper’s Ready, or Firth of Forth, or anything, really.
I have seen Yes do Close To The Edge, and Topographic Oceans, not to everyone’s taste, obviously, but the standard of musicianship was breathtaking, Chris Squire was an incredible bass guitarist.
I grew up on prog, the first proper rock album I ever heard at school was King Crimson, so I appreciate the skill of the musicians who play it.
However, there was an awful lots of over-indulgent crap produced as well.
Getting back on topic, I’m unlikely to ever hear Harvest Festival or Green Man by XTC, or Dum Dum Girl by Talk Talk, sadly.
And the thought that I never had the chance to see Sandy Denny perform Who Knows Where The Time Goes breaks my heart. 🙁