All that said, if LEP had lived up to expectations ED would have 3 separate builds now. I don't think that would have worked out well for the community.
I understand what you mean, but I can see ways around that.
If further expansions are cumulative (ie you have to own all the previous ones to get the latest) it would be fine for the LEP owners but could be frustrating for a non LEP owner to have to buy content they aren't interested in to unlock the content they want.
However if we take these examples of extra content, some can be independent of others:
Spacelegs: you don't need to be able to land on any planets to be able to float around ship-to-ship, or walk in docks & stations.
Non-atmospheric planets (Horizons): this is obviously independant of both spacelegs & atmospheric landings.
atmospheric planets: wouldn't require spacelegs but logically would require Horizons ie it wouldn't make sense for a ship to be capable of landing in an atmosphere & flying in space, but not landing in a vacuum.
The way Horizons has added content like multi-crew, SLFs & the Beluga (all horizons season content, but not dependant on planet landing) doesn't suggest to me that FDev have an independent, branched plan in mind though, it suggests a cumulative approach.
So either ultimately the LEP turns out to be a good buying decision & the non-LEP players become frustrated (the opposite of the current situation), or there will be minimal extra paid, cumulative content in future, leaving the LEP owners feeling like suckers.
I hope for independent expansions, where the LEP owner just gets it all, and non LEP players can pick & choose, but as you point out, it would be a more challenging path for FDev to follow.