Just a thought…
No one knows what the etymology for Ryukyu is. All we know is that it came from Middle Chinese 流求 (MC lɨu-ɡɨu). Also, there obviously was a substrate of Austronesian in Old Ryukyuan.
So assuming Ryukyu is of Austronesian origin, what would it have been?
In this thread, I posted examples of Austronesian words in Old Ryukyuan.
words related to celestial bodies in Old Ryukyuan, attested in texts such as Omoro Sōshi and Konkōkenshū, are Austronesian in origin.
OR Pangcah PAN Comments sun, sky, heaven, deity tidaN cidal *siNaʀ tadengal in Pancah means day break sun shine, ray, beam sino mi-cidal *siNaʀ heaven kawa kawas *kawaS moon ora folad *bulaN
In the *bulaN > ora example, we can see final N is dropped, as well as l > r.
So if we work backwards, I think it’d be possible for Ryukyu to be cognates with the Paiwan word for orchids, ljangaw, aka Liang-kiau, aka 琅𤩝, aka present day Kenting.
I think either it came from *Raŋaw meaning creeping vines, which orchids have that, in the wild they climb on trees. Or may be it came from *laŋkaw meaning tall, high, or lofty.