Chrome doesn't notify for now. that might change in future versions, but it seems the whole policy is here to stay. also chrome is the most used browser and its updates spread quite fast. in a few month chrome66+ could represent 60% of the market (https://www.w3counter.com/globalstats.php?year=2018&month=4)
Regarding PICO-8 games specifically, if audio is denied at start it won't ever resume. that might get fixed on the pico-8 side eventually. but I'm quite sure that most games here won't ever get an update. So, I think that disabling autoplay for all existing pico-8 games on the site would fix the problem. then devs that can handle it by themselves could re-enable it if they want.