I would love to see Qui-Gon show up as Force ghost (and not a flashback, I really wish flashbacks weren't a "thing").
It could make narrative sense too, and not just be a gratuitous cameo. A great thing to see would be Qui-Gon convincing Obi-Wan that the prophecy is still in play. It would fill-in why Obi-Wan would be so eager to give Luke his father's saber, and introduce him to the Force (when he was old enough). Considering the disastrous outcome of training Anakin, you'd think Obi-Wan would be reluctant otherwise. It could tie together the tragedy of RotS and the hope of ANH well. Ah, one can dream.
Also, my jab at TPM was a friendly one. That movie gave me too much to enjoy, to ever hate it. Nowadays, it seems even more enjoyable.