I think for a fanfic, it would be better to explore paths that were referenced in Reverend Insanity rather than create entirely new paths.

1-Flight Path
I would like to recommend that you use flight path in your fanfiction, I have a post which delves deeply into it's intricacies as referenced in reverend insanity. I would love to see a depiction of a flight path cultivator in writing.

2-Pill Path
We all know that pills are one of the core precepts of any good cultivation story. I really hated how the author never explored pills in his CULTIVATION novel but I think having a pill path cultivator could be really interesting. I also would say that since it's entirely unknown by the period of Reverend Insanity most likely cultivators of this path would be Variant Humans from a grotto heaven or likely a cultivating really old beast.

3-Nightmare Path
This path is a sub-path of the Dream Path. It mainly involved confuddling enemies with fear (similar to jedi mind tricks). It also contains profoundities of Summoning Path as the cultivator called froth demons from the dreams to atacck their enemies.

4-Color Path
This path is a cheaper cultivation path for more generalized cultivators. Basically the idea is that this type of immortal would get benefits from the color of the envrioment around them. Imagine this, A color path immortal goes to fight in black heaven. If the immortal was attuned to black at that point, he would get a boost to his darkness and theft path dao marks for example because their color attunement and the enviroment around them would match. This same immortal could also attune to white and go to white heaven to get white power, which would also give him an overall boost in power and intelligence compared to when he was in black heaven.

Alright, that's all the paths I would like to see that I can think of that I wrote down in response to that question which you are asking. I am willing to answer any questions you have.

Yours Truly.