Even if DCC decoders came in cornflake packets, it would still be tedious to address individual coaches/trucks to activate a tail light. Instead I suggest using electrically conducting couplers, which need only conduct well enough to pass a signal not power. Then each coach/wagon could detect if it was coupled at one or both ends. Further a very simple signal (on/off) could be passed along the train. Then when a loco turned on its tail light, it would only actually turn on the light if there were no attached vehicles, otherwise it would send the 'on' message along the train. Then only the last vehicle would actually turn on its light. Vehicles which would never be at the end of a train could just have a piece of wire joining the conductive couplers. It seems to me that the electronics needed to manage this on each coach/wagon would be rather simpler than even the simplest DCC decoder.
Any takers for this idea?