So in the absence of a better explanation I have to assume that ED's motive with decay is to enforce regular play, otherwise their design goals could be met by activating decay when you're online as opposed to off. As stated ad infinitum this unfairly penalises casual players. Welcome to the grind train!
It's a shame, it really is. Many games have tried this and it's always been met with almost universal ire from users.
Why penalize the people who are playing average gaming hours? They're the majority of the player base.
This is not real life; I do not have to make a regular play commitment to keeping my progress intact in a video game. Making people feel forced to play your game is a surefire way to make it a chore, which in turn makes it no more fun than doing the dishes or mopping the floors.
This said I hope Frontier realizes what a massive error this is and rectifies it before public release.