With a USB-C-to-microUSB cable, and the right little adapter, you can make your own, today.
Apple Lightning to microUSB adapter
This tip is short and sweet. Instead of dropping $19 or $35 on one of Apple’s cables, buy Apple’s microUSB to Lightning adapter instead. (At $19 list, this is even more outrageously priced than the cable. However, it’s a much better buy. You can use the adapter for much more than just connecting an iPhone to an iPad.)
Then, just add the Apple adapter to a cheap microUSB-to-USB-C cable, like this one from Amazon, and you have a fully functional Lightning-to-USB-C cable.
I tried it this morning. Not only does the iPad charge the iPhone, but it also lets the iPad import photos from the iPhone, just as if you were using the Camera Connection Kit and regular Lightning cable.
You also could use a third-party knockoff of the Apple adapter. But then you would run similar risks to using a knockoff Lightning-to-USB-C cable.
If you have these parts already laying around, try it out now.