So
A new use of the word so has arisen. Traditionally, so introduces an idea which follows from what precedes. Definitions in Oxford Dictionaries include ‘therefore’, ‘and for this reason’, ‘with the result that’. For example, I sometimes use so to begin the last paragraph of my posts – introducing a conclusion which follows from the facts I’ve presented:
But in a newly fashionable use, so introduces answers to questions. More widespread in the US but rapidly catching on in Britain, it’s particularly noticeable in TV and radio interviews. A couple of British examples:
A: So this is a political game.
A: So, there were elements of this that I really did love.
Before this fashion arose, such speakers may have introduced their answers with well instead. Well is described by dictionaries as ‘used to begin a story or explanation’ (Merriam-Webster) or ‘to show that we are thinking about the question that we have been asked’ (Cambridge).
Question-answering well is slightly informal: it has an air of improvisation, sometimes indicating that the speaker is thinking up an answer on the spot, 
rather than knowing the answer already. But so, as we’ve seen, is associated with conclusions that follow from known evidence – which suggests not improvisation but rather command of the facts.
It’s perhaps unsurprising, then, to hear this new, question-answering so in formal settings, from speakers of seniority. Here is Janet Yellen (69), Chair of the US Federal Reserve, described as the most powerful woman in the world, testifying before Congress:
breaks to the families of the top one percent?
A: So, I’ve indicated that I share your concern
resolved in an orderly fashion?
A: So, the living will process is something that’s
intended to be iterative
A: So, I’m not sure if that’s true
in which incredible economic and political power
now rest with the billionaire class?
A: So, all of the statistics that you’ve cited are ones
that greatly concern me
So, will so replace well?
So, I don’t know.
Further notes
It seems that the question-answering so is more often followed by a pause or intonation break than the traditional ‘therefore’ use. Even with its less improvisatory air, it clearly can be used (like well) to buy time.
It is interesting to read how you relate this habit to “evidence” and a “command of the facts”. I first became aware of this habit listening to scientists being interviewed on Radio 4 (Infinite Monkey Cage? More or Less?) about four years ago, where evidence and command of the facts is part of their empirical approach. I didn’t realize that it was originally a habit for American speakers.
Interesting. I can’t honestly remember when it first struck me; but it seems to me more widespread on the American TV channels than on the UK ones, and less skewed to younger speakers. It would make a good student project, because it’s pretty easy to track comparable talk shows, press conferences etc back in time on YouTube.