If they are planning to truly make a Junkenstein’s Lab style all heroes with talents but no switching mode. That way its always on the live game/main launcher available to all, everyone can enjoy it, everyone can keep feeding back on it, they can patch it frequently and make changes, and keep the mode playable permanently until it is ready to release as a true new PvP game mode.
Never confirmed this is the groundbreaking change but many are speculating it will be and I’m one of them.
Just throw it straight into the game and let people have fun not knowing everything for a while.
I hope it’s talents and it comes with season 15
Removing PTR/Experimental is by far one of the absolute worst things OW2 did.
We would’ve never ended up with messes like S9 or Mauga’s comp release, or at least they would’ve been better.
Combine Experimental with Mystery Heroes. Might be cool 
We had ptr/experimental when we ended up with mercy 2.0, brig launch, sigma launch etc. I’d be happy if it came back too as it just meant trying the balance changes and seeing them before they went live. But they very rarely made changes from ptr before hitting live, and seems to have been done mainly for stability reasons.
And mauga launch was after the weekend of testing for him anyways, so they buffed him based on the data, given they certainly did overbuff him before hitting live.