Good news! Official support to R5S and R5C has just been commited to git!
https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=c06a71f0b3fae00dbd402840ea6e3b532c35b0da
https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=4e09722a68825274048806c37a405eb3ee25500c
Thanks a lot to @1715173329 for your amazing collaboration and to @hauke for reviewing the code! 