Seems to me that Beekes is talking through his hat, no less than Deborah Steiner through hers. That “Ἰόνιος supposes “a shorter form” *Ἴονες” is a pure petitio principi, with nothing that I know of to support it and everything against it, not least the consistently different quantity of the iotas. The same goes for Ιονιος being a “reshaping after χθόνιος.” A reshaping of what, pray? There never was a *χθωνιος. So I stand by my (and the Greeks’) naïve belief that the Ionian sea, like the Icarian, got its name from the myth.
I agree with you (and disagree with Beekes who took it from Frisk). Beaumont’s reasoning seems quite sound: Ἰώ was probably an Epirote nymph, which would corroboratively explain the transmission of her name into a local geonym. Moreover, as you say, it is unlikely that long iotas and short ones, respectively, are there by chance—hardly even metri causa (like ᾱ in Ἀπόλλων in Homer).
The follow-up question is obviously the etymology of Ἰώ, but most likely it will remain unrecoverable.
Deborah Steiner is totally strange to me. What has she done?
Have a look through the discussion in this thread before you revived it, where all this was thrashed out from the top. And Deborah Steiner you can google. I like her.
I apologise. I had read the whole thread before reviving it, but somehow missed the name Deborah Steiner indeed mentioned above. The lemma in Beekes was wrongly represented (although we still disagree with it) in this thread, which is why I reopened this.
Timothée, I’m the one who should apologize. I thought you’d missed our recognition of the different quantity of the iotas (in addition to the ο/ω) and the sole residual query about Io herself. It’s good to have your support, for I suspect you know more about linguistics than I do, and I don’t have the reference books to hand. I didn’t know of Beaumont, and I very rarely use Beekes, and while whenever I’m interested in a word’s etymology I find I have to consult Frisk along with Chantraine I find him much more unsatisfying—and of course both of them are badly out of date. In this case I didn’t consult either, and mostly I stay away from the whole area.