When the reference is a timestamp, that comes from the Jeff Kaplan / Seagull interview on July 18th (Seagull & Jeff Kaplan: NEW Hero Confirmed! - YouTube).
The matchmaking and rating system has gone through a year+ long overhaul (00:54:30) to prepare for the new competitive ruleset (Introducing Role Queue - News - Overwatch), and I will describe what we know so far.
Season 17 will be shortened, and end two weeks early. After this, there will be a two week beta season, for the express purpose of testing out role queue (Introducing Role Queue - News - Overwatch).
Players must queue as tank, support, or dps (or some combination of the three). When a match is made, they will be given one of the roles that they selected, and will not be allowed to switch roles during the match.
There will now be three MMRs and three SRs (00:10:00). There will be one MMR/SR for tank, one for support, and one for dps.
Blizzard has been calculating each player’s role MMR for the past several months (0:08:02), though it hasn’t been used in matchmaking yet. This MMR will be used to seed placements for Season Role-Queue-Beta (00:14:27).
There will be no reset. Blizzard recently did an MMR reset for their internal test server, and it went about as badly as expected (00:15:40).
There will be five placements for each role (01:10:30). Playing all roles is not required.
There will be four leader boards, one for each role, and a combined one. To qualify for a leader board, a player must play 25 games per role (for a total of 75 if they wish to qualify for the combined leaderboard) (Introducing Role Queue - News - Overwatch, 00:23:45).
SR decay is gone (01:12:20).
Below are some additional interesting topics.
MMR used to be one value per mode (now it is three for modes that have role-queue). SR has not, nor will be, used in matchmaking (00:08:40). However, Scott persists in acting like SR is what matters, even though it is not technically true. Frustrating.
Stats are used to figure out when players are throwing (00:11:40) .
Role queue will be implemented in quick play as well (with separate MMR) (00:31:45).
Don’t take PTR too seriously. It is there to check for show-stopping bugs. Match quality is poor, and MMR/SR is inaccurate (00:52:00).
Applicable arcade modes will have role-queue (00:53:50), but not Mystery Heroes (01:08:30).
Sigma is coming (00:56:40).
Hero bans are not planned at this time (00:58:00).
SR is not used in matchmaking (01:13:30).
MMR goes from -3 to +3 (plus a bit for extraordinary players) (01:13:40). That is, MMR is in units of standard-deviations (a.k.a. sigmas).