Why not just use standard time, and shift schedules so that standard office hours are from 10am-6pm?
Also, it would be a shift to an 8-4 working day, right, if we were going to keep the clocks on standard time year round?
You'd have to re-negotiate every time you work with a new client. Are they on 9-5? Or 10-6? When can we schedule that weekly call? Businesses have no incentive to go through this headache, so they won't.
We already shift our working hours twice a year with practically no issues. Let's just not switch back once.
My experience is that these meeting coordinations still have to happen. Even within your own company, in the same office building.