Take this rumor with a grain of salt, you should. Cosmic Book News is reporting
that Yoda will appear to Luke as a Force ghost in Star Wars Episode VII to warn him about "a rising unbalance in the force and the need to preserve the Jedi." That sounds like a pretty standard rumor...but then it gets bigger.
There is also talk amongst production that would give a nod to the previous Jedi characters in the form of holographic pictures in the new Jedi Temple.
It's said it wouldn't be anything major, but would be in a background sequence featuring holograms of Yoda, Alec McGuiness as Obi-Wan Kenobi, Liam Neeson as Qui-Gon Jinn, Samuel L. Jackson as Mace Windu as well as others.
Such a background sequence would certainly be an easy way of incorporating saga alumni who are interested in returning to the franchise, which several