This will be a long thread, TLDR is at the end.
The hero release schedule.
There was nine months between the release of Sigma and the release of Echo. With this in mind, we could assume that Echo was released at the “mid point” between the previous new hero and the intended release of Overwatch 2.
If this was the case, Overwatch 2’s intended launch date would be somewhere around right now (9 months since Echo’s release).
The leaks.
Several “leaks” have been made since Overwatch 2’s announcement in November 2019 (here is a thread compiling them) that suggest the release date was in 2020.
However due to the pandemic, it’s almost certain that development has been pushed back several months at least. Should this be the case, we could expect to see OW2 (launch or beta) between February and July 2021.
So when can we see Overwatch 2 beta?
My guess is beta in February 2021 that releases at BlizzcOnline. Why? Because they let in-person attendees try out Overwatch 2 at Blizzcon 2019. It would make sense to allow attendees to try out the beta this year. And because it’s literally impossible to attend in person this year, we can assume that beta will be available to all online viewers.
I believe the beta will either run until official release of the game, or the beta will run periodically for 1-2 weeks with several iterations and updates before the launch. This gives the devs time to tweak balance of new heroes, reworks, talents and fix glaring issues.
Okay, what about the actual release date?
I’m saying March - May 2021. The Overwatch League has had it’s next season delayed until Spring 2021 (March - May is Spring), and I believe a big factor in this decision was to align with the launch of OW2. The pros will need to either be given access to the game early and be kept quiet, or the new heroes will be locked out of the pro scene for some time.
However, the official reason for the delay is "This gives us a little more time to plan than when we typically started in February. It also gives us and the teams a little more opportunity to deal with all the logistics and be ready to hit 2021 running when the season begins.” Obviously OW2 would not be mentioned, as this would essentially ruin the surprise.
TLDR:
I believe the beta will release at BlizzcOnline in February 2021 due to my belief that Echo was released at the mid-point between the release of the last hero (Sigma) and the release of OW2 (now). However the game is delayed due to the pandemic. It makes the most sense to release the beta at BlizzcOnline.
The full game will then release a few months later and align with the start of the 2021 season of Overwatch League.