Many openwrt users hope that openwrt support nanopi r2s.
I come to the same conclusion, it will be a killer device for the price.
I have posted to the developer forum, to ask if a developer is busy or plane to add openwrt support.
I have already order a nanopi r2s, I will try frindlywrt (frindlyarm openwrt fork)
Other on the forum have ordered the nanopi r1, openwrt work already on it. Check here Add OpenWrt support for NanoPi R1