I also found this video on YouTube talking about a lot of unused and cut ideas from TFA.
https://www.youtube.com/watch?v=TYLZhDTITr0
(Probably a lot of other videos on this subject, but this is the one I came across first.)

A few ideas that they were considering for TFA that I haven’t seen anyone talking about here before;

At some point Kylo Ren was essentially Vader’s replacement, and he would essentialy have both the same name and a similar mask. This was apparently meant to suggest that “Darth Vader” was his title as opposed to the whole Sith thing that the PT came up with.
(It’s possible that this idea was rejected for contradicting the PT.)

Another idea that they seem to have toyed with was including a Vader/Anakin hybrid-Force-ghost. Essentially half Hayden Christensen, and half Vader’s mask. I guess this was the basis for the rumour about Christensen appearing in TFA came from.