@hippy is meaning that Supernova rear lights won't work with B&M/Schmidt front lights because they send AC to the rear lights, unlike the DC of the Supernova (as you noted).
I think that's what you miss out on - the LEDs will naturally rectify the AC input and light up but the stand light's capacitor won't have any rectifying circuitry and so won't charge up.
@hippy is meaning that Supernova rear lights won't work with B&M/Schmidt front lights because they send AC to the rear lights, unlike the DC of the Supernova (as you noted).