Dingoonity user Soul_Est has opened up a github for opendingux ingenic JZ47xx devices for developers to come and join and get opendingux booting from SD card. If you fancy having a go and have the know how why don’t you take a look and see if you can get things running from the link below for a start the RS-90 really needs external boot to proceed further with any type of opendingux.
https://github.com/SoulEst/OD_on_JZ47xx
OpenDingux on Ingenic JZ47xx Devices
This repository and the accompanying wiki are meant to serve as repository for research into building, booting, and optimizing OpenDingux for various devices containing Ingenic XBurst 1 SoCs.
To help out with the research please, either send a Pull Request, create an Issue, or post on the thread on Dingoonity.org.