I personally never found a nougat SDK for RK3288, only for other rockchip devices that I am not sure if it's usable for RK3288 or not (never tried because I don't own an XD anymore).I guess the main point is to find a public nougat SDK for the rK3288, if Phh knows where to get one, I guess anyone interested can begin to try stuff, because kernel is available. I am not sure if there are active devs with an XD that are interested or not. During my legacyrom times, I was alone in development for GPD devices until XD+ (device that I also made some contributions too by the way).
Anyhow, the main thing is to get a RK3288 SDK for nougat and that an active dev who owns an XD want to start developing stuff.
If someone wants to try, I don't mind to take a look to some stuff to help, but that's it, because I retired from android development and now I am in another projects non android related and not by the name of Skelton.