I took a deep dive into this question, and the answer is: kinda, mostly, yeah! CSS + HTML (duh) + user input is Turing complete. Is it possible to remove the user input part? Then I can re-title this post to be more, ahem, declarative.
My talk and I are going on tour this summer! In other words, I submitted to a bunch of conferences and got into some of them. So stoked!