I’m a little baffled by this one. File upload isn’t exactly some new HTML5.1 feature or anything. There’s no good reason they can’t have this handled properly.

EDIT - just for some additional context, I've never used this feature so I had no idea it was more than a mere file upload. Looks like Discord has chosen a non-standardized API that's currently only in Chromium, but if it were up to me I'd try to budget some time for a simple fallback in case someone's using Discord in Safari or FF.