Why not just a micro-USB one? Why waste an expensive lightning cable for this?
While I've long complained about Apple making their own standards for even the smallest things, I have to say that Micro-USB sucks compared to Lightning. From its water-resistant standard to its reversible connection, to its basic build, it's more durable and long-lasting compared to Micro-USB.
As a desktop tech, while micro-USB cables are dirt cheap, I can't tell you how many times someone broke the female Micro-USB port on their BlackBerry or Android phone, and that is the costly part to fix or deal with.
I bought the
Aukey portable battery on Amazon (the only one with the female Lightning port) and I love the fact I don't have to carry both a Lightning cable and a Micro-USB cable everywhere to charge the iPhone and the portable battery.
I can totally see Apple making an Apple Watch portable magnetic charger disc with just a female Lightning port. That would be key.... key... keychain! If they made a keychain Lightning cable connector like the Nomad, it would be a complete package to charge either!