I think with the size of USB-C and Lightning, we are pretty close to the point (if not there already) where structural limitations are not going to let us go much (if any) smaller. No one wants a connector that will break after 10 uses.

USB-C, electrically, has enough headroom that performance should not be an issue for a very, very, very long time. Already you can push more data over a USB-C cable than a phone can meaningfully handle.

The only thing that really comes to mind is we could go to fiber core for crazy data speeds but those are so delicate I don't think the improvement would be worth the hassle unless we have a big improvement there.

I think C could easily adopt a fiber, there's the "tongue" bit in the middle of the socket, and empty space in the middle of the plug, could easily have a fiber run down the middle there.

There are literally USB-C cables with fiber cores, right now... on the market.

A USB-C cable with fiber core is what Oculus Go suggested to connect to a PC.

Those use a converter in the cable itself though right?

The difficulty isn't in fitting the physical fiber, they're tiny, it's in the delicacy of highspeed fiber optics.

Standardization also improves user experience. And it does so here and now, as opposed to some hypothetical future gains.