I just volunteered as a candidate for duty officer, but I had to include one caveat about a bullet point in the duty officer description: I can't IRC well. At all. I would be afraid to monitor IRC and be available to answer questions there because I would be afraid of sending a private response to the entire channel. So, I am all in favor of using more newbie-friendly communication channels (like Slack).
(As an aside, I suggested that I would be fine with IRC if I could practice in advance. A toast to feeling inadequate about not knowing how to do something, but doing it anyway!)
I think my main issue with Twitter is that I definitely notice my attention span shrinks if I use it regularly, and I want to be able to use more than 140 characters to ask my tech (or other) questions. I feel like most of my Twitter responses amount to "Look at this URL" instead of me formulating a response tailored to someone's question. ("Which ILS do you use?" "We use ... Hey! Look over there! Shiny Object!") This is not a criticism of those of you who can do it with ease; it's just to say that I think listservs are still useful in a lot of ways, if we can just get people to accept the risk of asking questions in public.