Adding a second usb port to get around current limit
You can only pull more than 100mA after your device has been configured. For a single port device that isn't much of a problem normally, you just declare your power requirements in the configuration descriptor and either the host activates that configuration (and therefore allows you to use the power), or it doesn't (then the device doesn't work) and shows a dialog telling the user to use another port.
For two ports, that means you need to implement two USB devices that each request 500mA, and only activate the full brightness if both were activated. That's a fairly complex setup.
Instead, I'd go with an external 5V supply with a barrel jack connector, and a buffer IC between the keyboard controller and the LEDs, so the data pin of the LEDs is driven from the same power supply as the LEDs themselves (the SK6812 are a lot more resilient than the WS2812, but they still don't like it when the data pin is at a higher voltage than the supply pin).