Good question! Just tried it on my 2017 EX and its just for charging. Apple CarPlay did not recognize my phone through it. I guess that makes sense because then what would you do if two different phones are plugged in?
The two ports are only a couple feet apart so theres no reason you couldnt run a longer cord to anyones phone for CarPlay.
I just like that it is in the console hidden in case I leave it in the car. I wouldn't mind only being able to use one at a time if they both worked. Maybe someday I'll make a modification to swap the two so the front one only charges. Not sure if it will be difficult or not but I'm going to keep it in the back of my mind.
By extensions I mean like add a usb hub to it so more than one thing can plug in.
I searched the manual. I couldnt find an explicit prohibition against using a hub or multiple devices, except a warning that using it for media purposes might prevent the car from accessing the music files. However it does note that it?s a low power port and may not support rapid charging on devices, so I would think if you end up splitting the power to many ways it will become barely useful or possibly damage the port. Youd probably be better off just rotating between devices that you need to charge.