You could get more gears on a Trivelox type system if rather than keeping a constant spacing between all the sprockets and moving the whole cassette, the individual sprockets move in relation to each other so only the cog in use has space either side for chain clearance and the rest of the cogs are collapsed/abutting each other. I have a design for it I sketched a while ago but it’s operation might be a bit problematic when covered with crap etc.