Joining many others in the extreme disappointment that is becoming regular with MS these days. Here are a list of things that will not work in Edge and there is no 'GOOD' replacement for these. Please consider extending this date, I can't even begin to explain the amount of work it will take to get people to not use 'open with explorer' since as so many have said, working with files in SharePoint is a joke. Honestly I think I will be pushing my company to move out of SharePoint when that goes away, sync is not a replacement and actually causes more issues!
 
- Open with Explorer (and mapped drives since they require IE 11 auth?)
- All Office files open in the browser by default (regardless of the SharePoint online setting that says 'open files in the client by default' lol)
- InfoPath forms will not open in Edge (do NOT tell me to migrate all my infopath to powerapps, even if that had full feature parity which it doesn't, you're giving us so little time to migrate them) 
Extreme disappointment with MS, I used to be the guy that supported/defended you at my company... your actions over the last 2 years have actively turned me into yet another employee saying "why are we staying with MS?"