No update to make, I got distracted and haven't got back to working on the lighting beyond what's on my
Car Light Board page (the third page in that section, describing work from last summer). Also, Kato's new interior lighting kits, at least in the newer trains they're designed for, have much less flicker than the older ones (I still have several trains worth of the old ones to de-flickerize, so I still plan to get back to my circuit eventually). Going forward I'll be buying their new kits exclusively, even at a slightly higher cost.
On DC, the LEDs would need more voltage to light in my circuit, as you lose 1V in the rectifier and (with Kato) about another 0.75V in the resistor. That's enough to be a significant nuisance, and since the capacitor won't charge above that voltage, the "ride through" time would be much shorter than it would be in DCC with a 12V track supply. However, I didn't play with this on DC so I don't know how much effect those factors have.
The same basic circuit should work for Tomix if you can get it between the track power and the lightboard there (it's designed to take DC or AC and convert it to DC, charging a capacitor that will discharge into the lightboard when track power drops below the capacitor level). But I haven't tried it with anything other than Kato, and there are potential issues if power draw was much higher (Kato uses SMD LEDs that draw ~5 mA, where standard LEDs draw 20 mA and bulbs draw 60 mA; it probably wouldn't work with bulbs without some alteration and the benefit even on standard LEDs would be much reduced by the higher current draw from those).
