USB was originally designed to be a universal connection (replacing serial/parallelFirewire ports etc.) but it has changed over the years and I think there are now 10 different types (including microUSB). Not to mention Apple's Lightning.
When does it all end? How could a train have truly universal charging points if there are so many different types of USB?
How long will it be until we have wireless charging?
You do what every supplier of USB power sockets does, provide a USB-A socket (the "socket" end that everybody is used to, their laptops and phone charger adapters will have one) and expect people to have the right cable to connect whatever it is they want to charge.
The only current theoretical change to that is USB-C to USB-C becoming commonplace, which won't happen in my lifetime, not least because its biggest proponent (Apple) will be reluctant to give up their business of selling 20p connectors for 20 quid while everyone else buys their cables in Poundland.