I did a quick look on rollcall last night, before all the matches were even logged for the day, and there were 18k+ total matches for the day (granted it was a sunday).
So if it were br+/- 0 that would be a relevant match on average (at your specific br and specific nation) available every 1.6 minutes.
Obviously there are nations and BRs that are more popular than others, but that would change with no uptiers, since BR4 (and BR1) would not be afraid of constant uptiers, and nations would probably fill out more evenly over time across the BRs and be more even overall.
The matchmaking could also be conditional, as in reverting back to the current system if no match is found in 60 or 90 seconds. Which would give you the option to cancel at 60s and re-queue if you really didn’t want an uptier, or to just stay in queue if your priority is just to play a match.
Additionally, BR1 matching with only BR1 will undoubtedly help with noobie retention, increasing the total amount of players and matches over the long-term, reducing the queue time.
Just my coupla cents.