Relatedly, this blog post, "So you want to abolish time zones"[0] elaborates a hypothetical scenario of calling someone in Melbourne, and how complicated it would be without time zones (since if it's 4 am everywhere, what's the solar time in Melbourne)? I find it hard to imagine a time zone-free world in which you wouldn't also need a reference for when solar time happens in different regions, which would just end up being a messy version of time zones all over again.
Various global organizations and groups already use UTC to coordinate, so it seems we already have an opt-in solution for those who really need to abolish time zones.