There's a reason why Destiny 2 is not up for pre-order on Steam. It's clearly on either Bungie's own launcher or Blizzard's. There are already a ton of Blizzard launcher users so having Destiny 2 on there makes a ton of sense for Activision IMO.
I mean the majority of my PC gaming friends are actually Blizzard-only. Blizzard having their own launcher didn't get the shitstorm that Origin did because a lot of their fans only play their games...and Blizzard is very good at keeping you in their 'ecosystem'. There's this assumption on GAF that PC gaming = Steam but that's very much not been my own experience. There's this whole section of PC gaming that got drawn in by Diablo 2, Starcraft and Warcraft 3 and never really went past Blizzard games.
But unless Blizzard is actually involved in Destiny 2, it would make no sense to re-brand their launcher so soon before adding a non-Blizzard game to it. While I'd actually like to see more Blizzard influence in Destiny 2 - they solved many of Destiny's problems like raid LFG tools in WoW years ago - I can't see a situation where they collaborate to that degree.
I always did think it was funny how Halo players called bungie.net 'bnet' when that's what people called battle.net, though.