There are no details. This is all that was said:
People are focusing on McCree and Rein for whatever reasons, but there’s nothing to say that Ana, Orisa etc. won’t also get changes. Given the experiment where BOB was sleep immune, I wouldn’t be surprised if the devs had reservations about Sleep Dart.
On the other hand, it could be like ChibiFox says in that thread, and instead they’re considering anti-CC passives or the like for tanks.
The only thing we’re sure of is that we don’t know.