I think he would say that the "nowcast" is so useless and deceptive to be malpractice, since everyone will interpret it as a forecast, and even if they didn't it's not in any way useful. Which I agree with (unsurprising since I've semi-invented it as an opinion for another person).
It's only useless and deceptive if you willfully do absolutely nothing to understand what it is, or how it differs from the other models 538 has, which apparently is the case for Taleb.
Or in other words, you're 99% of people who will ever hear the number
It explains on the website what it is. And if you are going to rail against something, you should understand what you are railing against.
Silver has said before, at least in the podcast, that everyone at FiveThirtyEight hates the nowcast and its various incarnations but I think there's some pressure from the business side of things (for views, likes, shares, etc) to have something volatile for people to eat see day in and out.