While the old post-ROTJ EU novels pretty much wrote out the force ghosts right away (by having them sort of pass to an even higher plane of existence) in Heir to The Empire, the sequel trilogy has kind of had two....
1) Obi-Wan's young and old voice in Rey's vision ("Rey, these are your first steps") with new dialogue by Ewan Mcgregor.
2) Of course, Yoda showing up and able to actually have some impact on the physical world.
Some people think we might get a Luke force ghost in IX as well, but what about Anakin/Vader? During one stage of TFA this was apparently considered, as there's some concept artwork depicting a sort of half-Anakin/half-Vader ghost (something also used in the "Legacy" comics). Although many disliked Hayden in the PT of course, having him could work thematically and tie the three trilogies together, maybe having him appear to Kylo Ren or something (maybe perhaps helping him back into the light?) or even hanging out with Luke.