What about the
Panaplex 7-segemnt gas discharge displays?
Or the gas discharge dot-matrix displays that include their own 'sift
register)? You know how you can step a discharge round a dekatron tub,
I liked the mechanical project-type display, where a stepping
arrangement moved a strip of film. Probably a bit large for an Elf,
though.
Edge illuminated numeric displays (link shows a modern version... the old ones used grain
of wheat lamps):