He didn't say, & you said "if", and it doesn't make a difference.
In any case, TMCC, conventional, DCS, Bluetooth, WiFi, clockwork, Legacy, or Wizardry, the capacitor is not needed. If there's nothing on the track with the isolated rail, the signal is just not needed.
If there is something on the track with the isolated rail, the axles, instead of the cross ties, will shunt/short the capacitor anyway, rendering it useless/redundant/not needed. I'm not quite sure why Reagan spends so much effort on presenting this scheme.