Verified Games Statistics
This is just my napkin math on a recent sample from the number of games added from February 7 to February 11 ProtonDB numbers.
Valve adds 16 games to steam verified games a day. That would be 5840 games a year at this rate (3.3%) . There are 175,547 listings on the steam platform, so at this rate it would take 30 years to verify the current steam catalogue if no new games are added.
13,668 games are verified or playable that is 7.8% of current catalogue.
Plenty of games still run just fine without the verified status but its nice to know what the status of your games are before you hit install.
I don't think it would take this long to verify the whole catalogue as Valve would become more efficient testing games and will invest more into Linux as the platform is more widely used.
Sources:
https://www.protondb.com/
https://store.steampowered.com/search/?term=