I don't know, you'd still need to coordinate based on local time, let's say I want to set up a meeting with colleagues from different time zones at 10. I have no idea what time of day that is for them, are they sleeping, having lunch, etc. With time zones, I can look up the time offset, with universal time I'd have to check their location and what time of day it is for them, which could be confusing, how do you map it exactly, bed time, lunch time, one hour before lunch time, two hours after bed time?

The other problem is that I don't think habits would be easy to change. Right now people in some european countries want to stay permanently on summer time to have more daylight after work. We could just as easily stay on winter time and have everyone go to work earlier, shops could open at 7 instead of 8, etc. But for some reason this isn't considered, so I assume it's easier to enact all year DST than to change working hours.

You are joking, but I think City-based timezones would work well on today's internet. We have better than ever computers to do time math and scheduling/coordination for us, let's leverage that. It's easier than ever to go to more timezones rather than fewer, because we don't have to make train companies happy anymore and because some people would get better sleep if their local time was closer to their solar time and because DST is easier to get rid of with smaller timezones. (DST is, among other things, a hack around our timezones are too wide.) The IANA timezones are even already primarily city-based, so a lot of software wouldn't even need to update anything but their IANA tzdb.

Now might be a great time to do something like that. It doesn't sound like a serious proposal, but there would be interesting benefits to city-based timezones again in the modern world. We actually have the technology to scale smaller timezones now. We aren't relying on mechanical clocks like the train companies were and paper calendars like early multi-timezone companies like GE were. We could make local time resemble solar time a lot more again, and solve it as a software problem.

1. People who never collaborate globally/cross TZ vastly outnumber those who do. And the people who do can already use UTC right now.

2. Making everyone in the world to use UTC is going to make everything less convenient for everyone who lives a few hours away from the UTC TZ (i.e., most of the world). Because in UTC many of their daily events are going to span 2 dates/weekdays.

3. For the handful of people who need to schedule cross TZ meetings there's https://www.timeanddate.com/worldclock/meeting.html, no sign up required.

That was some of the arguments behind the interesting but failed experiment that was Swatch Internet Time: https://en.wikipedia.org/wiki/Swatch_Internet_Time