Or even better, they could have made the side-by-side feature work for any web pages at all as a more general layout feature, with some kind of easy access tool

Or even better, they could have made the side-by-side feature work for any web pages at all as a more general layout feature, with some kind of easy access toolbar to allow you to pop them in and out as desired. I think "Reborn" is a bit of a stretch here.