I guess that "so" in your last example is referred to "sodomite, sodomize". In The online etymology dictionary: "first recorded 1897 as a euphemistic term of abuse."
http://www.etymonline.com/index.php?search=so&searchmode=none

sod: term of abuse, 1818, short for sodomite

I'm not sure about so = sodomite. An expression my mother and her friends used was "one of those" - it was the kind of expression that went with a gesture, or had a meaning implied by context, as "so" might have done.

Yes, "so" seems like a very unlikely shortening of "sodomite", and Kate's suggestion seems very likely.

I've encountered the term a few times before in books set during that period (1900-1930 mostly, I hadn't realised it had come back into fashion in the 60's and 70's).

I always assumed that it came from 'so' as an affirmative pronoun - as in, "Is he ...?" "Yes, he is 'so'". (probably accompanied by raised eyebrows and a knowing glance. Pure conjecture, of course. 'so' and 'sod' have very different vowels, I'd be rather surprised if the two were directly connected in that way.

I could certainly see "that way" being used so.

E.g. "I have come to the conclusion that I'm not really 'that way' at all."

Yes, it's definitely 'like that'; I should have provided definition 7.a. as well, which is:
so-fashion adv., in this or that manner. U.S. dial.

I hadn't realised it had come back into fashion in the 60's and 70's

It didn't. Ackerley was born in 1896 and is presumably writing about the early years of the 20th century; the 1973 story is talking about Oscar Wilde's day ("as it was then called, ‘so’).

So "That's SO gay!" is redundant.

Heh.

Two posts above seem to hint that "so noble" and "so silly" might not be early examples of 'so = very' at all.

'So = thus = in that manner' could surely explain both, and therefore make them not prescient examples of 'so = very'?

Am I misunderstanding?

.

Doesn't work for me in either sentence. Theoretically, it might apply to the Richardson quote, except that I would expect the reverse order: "I looked silly so." And the exclamation mark virtually enforces the modern reading.

The Dutch can help you. In the seventies of the last century "zo" (i.e. the adverb "so") was still used in the meaning of "gay". As an inoffensive way of mentioning the adhaerance to preferring to live with the sin that dares not etc. This "zo" is not derived from Sodom.
Dutch knows "sodemieter" (a noun, meaning "fag", from Latin "sodomita" naturally), but the commoners in general have forgotten the origin and original significance thereof. E.g. the injunction (indeed a denominative verb here) "Sodemieter op!" means "scram"!
Shades of meaning fading away is common I guess. My father in law is a neat-language man and does use the word "leuteren", but frowns on "lullen". Both mean to something like "to talk nonsense". Both are derived from words that mean "penis", being "leuter" and "lul", but this meaning of "leuter" has become an unusual one and does not pop up in the mind when one uses the verb "leuteren", which is only and exclusively a designation of a verbal activity.

How about old "so and so" There goes old "-" as we do not wish to name names.

The comments on Dutch "leuteren" remind me of Am. slang "dick around" i.e. waste time.

UK speak: It was so not me, which means it was very unlike what I would normally do.

I just happened on a memoir ( http://www.counterpunch.org/cockburn04102004.html) of Claud Cockburn's, published by his son Alexander, which contains a lovely example of the usage:

it is certainly true that in the most flamboyant and "trend-setting" intellectual circles homosexuality was in some cases so nearly de rigueur that aspiring writers, artists, and above all actors, actually felt compelled to pretend to be homosexual. The slang word for it was "so". In reply to the greeting "How are you?" a common reply was: "So so, but not quite so so as sometimes." A friend of mine who had the most "normal" sexual tastes started a literary magazine which, it was immediately suggested, should have been called Just So Stories.