1: So
A familiar part of English speech is the locution ' .. so .. that ...', as illustrated by
He was driving so fast that he had no chance to make that corner.
Or:
She was so good at chess that no one wanted to play her.
The construct is something like: [Noun phrase] [be] so [adjectival phrase][relative clause]. This use of 'so' has it as a somewhat complicated adverb, intensifying the following adjective but also requiring a clause following the adjective ('that no one wanted to play her').
But now the word 'so' is often used simply as an adverb in its own right, like 'very'. 'She was so good!', etc. It's like a comparative that has lost its object. [JL points out that this is actually very old; nevertheless I think that its popularity has increased manifold].
I have often indulged in it. I feel its power. But I fear its effectiveness will be temporary. The effect it now has depends on listeners being aware of the comparative, that they will join me in half expecting it but being indulgent if it does not in fact come. They don't really care what in particular should take the place of the comparative clause marked by 'that', as it is intimated that some comparative could be articulated, and that is enough. Like an ellipsis. But that awareness, that expectation, will go. It'll just be like 'very'.
2: Really
(Yorkshire, Lancashire, ...?). When you've said that p—'The defendant was guilty'— but somehow not with the emphasis or panache you'd have liked, you can tack on 'really'. As in 'p, really'. 'The defendant was guilty, really'. Now if I'm not mistaken (a pretty big 'if', I grant), this is not just a vacuous phrase, but serves to express the speaker's being not quite at ease in speaking as they have just done. The word literally says 'Yes, that is the right word!', but what the speaker conveys is a certain dissatisfaction, as if the speaker did not quite succeed in expressing the meaning satisfactorily. It may be compared with '... you know what I mean?'. Or, it is as if one's turn to speak has ended too soon. I thought there was something more! ('Is that all there is? ... If that's all there is my friend..then lets keep dancing; let's break out the booze, and have a ball').
3: Rising Intonation
This is not strictly a matter of lexicography and not even strictly of grammar, but it is so distinctive and has appeared so suddenly that it's worth commenting on (to use 'so' in the old way). I reckon it's been with us for about twenty years or so in the speech of the young but it has become rampant in the general population for only about five years (correct me if I'm wrong). This is the practice of using a rising intonation—typically reserved for questions asked with the declarative form, as in 'You want the menu?'—for a genuine statement, an assertion, where the signal conveyed is normally (though not always) that the speaker is not done speaking; what follows is another declarative statement, or another declarative conjunct or disjunct preceded by 'and' or 'or'. Typically but not always again, the speaker will do this at the beginning of their turn, with the rest of their statements or clauses following the old conventional downward-tending pattern.
In writing it happens too, that a statement is made using the normal declarative, but a question-mark is added all the same. I assume as before that the speech-act remains that of making a statement, even if the assertoric force conveyed is thereby dialed back. Unlike examples discussed in the previous paragraph, it occurs typically not at the beginning of the piece of writing, but near the end. Often it will have the modal adverb 'maybe' (or equivalent) governing the main verb. For example the closing sentence of a comment in a thread might be, 'Maybe we ought to relax?'. I take it that that speech-act would be of the same category if the question mark were removed.
Another sort of example in writing:
He passed his hand over his forehead, a little wild-looking, as if he himself had suffered only a narrow escape. "I think about it every single day. I still see her face, you know, getting into that cab? Waving goodbye, so happy." (Donna Tartt, The Goldfinch, p. 215)
Of course Tartt was not writing an academic paper or a piece of journalism. It's a case of the author trying to be realistic in her reported speech, accurate to her imaginary protagonists—who in this case are young people in the US I think around 2010 (the speaker is Goldie, a Latino working at a parking garage).
Why has this phenomenon come about? As far as I can see, it serves two purposes.
The first, as in the example from Donna Tartt, is the benign one that it serves as a sort of conversational check-in: I imagine the speaker simultaneously looking up at into his listener's eyes, looking for recognition at an especially fraught or emotional moment of his speech. 'You with me?', or 'You feel me?'. It encourages intimacy, connection.
The second is somewhat more disturbing. Again the signal is to check in, but not normally with a look that beseeches intimacy. It signals a rather lack of confidence in what one is saying, either lexically or factually. It is not accidental that the tone is normally reserved for one of questioning. I can't help but take this development as a sign that it holds of mankind in general, or at any rate of a certain culture of English-speakers: it signals, across the age, a loss of confidence, of certainty. It's almost as if the very practice of assertion is slowly being chipped away in a minor Orwellian nightmare: Here are some words; I am not asserting them, I'm not saying they're true, I just raise them for consideration, ok? They came to mind. I'll take them back if you don't like them.
I would say that we have here the birth of a new variety of speech-act, of force, but we already have such devices as 'Perhaps ...', or 'I suggest that ...', and so on.