It did occur to me that you could design a telescopic seat pillar, with two preset heights, one for riding and one for getting on and off. It would be lightly spring loaded so that it would rise up with no weight on it, and a ratchet would then hold it up. Operating, say the rear brake would allow it to drop for dismounting. Once you were off the bike it would rise up and lock. Before mounting, you would pull the brake lever and push the seat down. Once under way, lifting your rear off the seat momentarily would allow the seat to rise.If prefered, a separate seat lever could be provided.Another possibility would be to just have a height adjustment lever filled under the seat, for rapid adjustment between two preset limits while on the move.
Or maybe, it would be a solution looking for a problem. It might be a help for older or less abled people.
What do you think?