USB 3.0 power and usb 2.0 data
From an official point of view, if you use a USB3.X Connector you should be able to get USB3.X Functionallity since in the USB Certification you would need to also test the superspeed portion of your device.

If a device is superspeed the D-/D+ lanes are NOT used for power, they are in idle state once USB3.X Traffic is going on.

So if not looking at the official standard, your implementation should work when using High Speed lanes and the Power of the USB3.X. but I would not recommend this !

Another thing I would like to suggest is using a Type-C(tm) connector and looking into the power rating of this, might be more suitable for your specific requirement instead of creating a Half USB3.X the power would depend on the hosts RP configuration(500mA or 1500mA or 3000mA)