By max altitude notation I mean having a very large, immediately visible number, on each bit of airspace; a number that summarises all levels of tiered airspace and gives me an altitude I can fly to without entering anything that is restricted.

I originally saw this as a additional file for XCSoar (heights layer), and have adapted it for use in the flight app I currently use. It means that I can just look at the moving map and can see immediately how high I can fly without entering any airspace. Using this I don't have to wait to be warned - which seems to me is analogous to driving a car along a route and not having speed limit signs, but just a warning when you are getting too fast !

Also I don't have to double check any control zones under TMAs etc (eg multi-levels of airspace). As far as I'm concerned the less I have to look down inside the aircraft while I am flying the better. I don't use SkyDemon at the moment in flight, but I find SkyDemonLight invaluable for planning. If this idea could be implemented (as a chart option) I would probably buy the subscription.