So, it seems to have started becoming hugely popular around five years ago to start a conversation with "So.." as a discourse marker. Not so much as in the question "So?" ("So..do you want to go to the concert?")
...but "so" as an answer or "conversation manager" or "interactional agenda."
One class I teach involves students showing and interpreting collages they have made.
I don't think five years ago any students started their explanations with "So..." Now, almost all of them do, regardless of age.
SOoo.. whatsup with that?
Linguists aren’t alone in spotting the trend. Journalists have caught onto the discourse marker in the past few years, spurring articles about the tiny word and its growing use.
The movie “That Awkward Moment” also called attention to the “so” that starts sentences. Zac Efron’s character coins the moment when a girl tries to define a relationship as “The So…” as in, “So, what does our relationship mean to you?” For the characters, the discourse marker signals trouble. link
So, many are blaming Mark Zuckerburg.
(This all reminds me of a previously-discussed shift discussed here: thirty years ago, no one would call the songs sung at a Christian gathering "worship" or "the worship time"...let alone that a "worship leader" meant the song leader. See this and this)
The discussion about "so.." as the new norm/normal often focuses on the grammatical approprietness and/or the thesis that is is lazy speech.
Excerpt below from Do you use “so” to manage conversations?:
Researcher Galina Bolden studied recordings of conversations, looking at the difference between the sentence-initial oh and so. In a 2010 New York Times article Anand Giridharadas sums up insight Bolden supplied via email: “To begin a sentence with ‘oh,’…is to focus on what you have just remembered and your own concerns. To begin with ‘so,’…is to signal that one’s coming words are chosen for their relevance to the listener.” If words like so and oh were used to arbitrarily fill a pause, they wouldn’t take on such different functions from each other. Bolden suggests here that the sentence-initial so is a way for the speaker to subtly cue to the listener that the following information is relevant to the listener’s interests. Whether or not the information is actually relevant is for the listener to decide, though perhaps this cue makes it more likely for a conversational partner to pay attention. (If you want to learn more, Bolden’s research is also discussed in this Language Log post.) link