Would be designing outlet panels with USB and DC coxal to barrel connector, AC connector would be next to it. Inside the panel, it would require something ridiculous like a 16farad Capacitor high pass filter, and 20H inductance low pass filter would get the dc close enough to regulate.
Cable thickness and length would be another issue, even if I went with a separate cable carrying dc the voltage drops over distance are quite nasty over 30m, I guess if I had higher voltages from a large number of solar panels in series and charged a battery close to outlets then stepped dc-dc, I guess that would be more efficient than dc-ac with an inverter and back to ac-dc?