Serious question, why not adopt one timezone globally? For some of us sunrise would happen at 10pm, for others on 4pm. So what? Wouldn't we just get used to it? Is there any rationale for anchoring start of the day between 4am-8am?
Timezones are a lot less of a problem now that we are using calendar apps to book events. Better integration of tools to negotiate availability would make that even easier.
The problem that people largely govern their activities by the rotation of the earth and we are in different places on that globe doesn't go away.
You would still need to do the effort of understanding what 10pm means for the other party. 10pm may be your lunchtime while it's the middle of the night for them.
If things really were more complicated and you always needed to ask the question of "when can I call today", would it really be that difficult to incorporate schedules into contact records so your phone can tell you "available after 23 today".
With timezones: google "what time is it in melbourne"
Without timezones: google "when morning starts in melbourne"
Didn't convince me a little