I don't know if this feature was pre-rolled to _some_ teams, but we've been using this for a couple of months at least (as far as I can remember). The answer to those who are wondering is: No, it does not support sharing control with the viewer (in fact, the viewers are just that, viewers). So don't throw your ScreenHero just yet.
How does it work?
"Ok for the most part". Like most slack, it has a lot of random glitches that are more often than not resolved by reloading the "native app". Sometimes this only works from the menu (Mac -> View -> Reload), because the keyboard gets frozen.
It's easy to use and it works fine more often than not, but don't expect this to replace a full-fledged screen sharing service/app, because it's not, at least yet, but since we have no clue what Slack's roadmap looks like, we can only hope/guess.