If one browser laggs behind then the rest shouldnt deploy?
This is crazy
[1] i am only counting major modern browsers here: chrome, edge, firefox, safari. you are welcome to support more, but these at a minimum.
Wtf.
Popular as hell services are constantly annoying users e.g reddit fb
Or arent or werent available on web at all - iirc instagram
If you have leverage then they aint gonna leave as hard as you make it sound
if it doesn't break then you have a graceful fallback which i did already suggest as an acceptable way to support new features in case they are not supported.
but if the site breaks in some way, it may prevent me to complete the objective on the site. if i wanted to buy something, and the site doesn't work because of that missing browser feature, then i will have to go buy somewhere else. it doesn't matter how much leverage the site has if i can't use it.
any feature that is not implemented in all major browsers should be considered experimental. it might go away. it's fine to use such features for experiments, but they should not be put into production and relied upon.
any differences in the implementation of the standard should be considered a bug. warning users about bugs is fine, but automatically redirecting me to some other browser that you deem working is not.