Comcast spent over two years experimenting with its Stream video app in the Boston and Chicago areas, before essentially juggling some content and renaming the millennial-targeted service as Xfinity Instant TV – rolling it out in beta mode to broadband subscribers in “select areas” this week. Going down the Go90, millennials-only route would be a glaring mistake, which is why Xfinity TV offers three additional packages on top, to resemble a service much more akin to something like Dish Network’s Sling TV or Sky’s Now TV in the UK. In short, Xfinity Instant TV is a staunch defense against AT&T, in both video up against DirecTV Now and in broadband, and the move is a precursor to the elusive main…