Honestly, I dont see this to be an issue.
I have 3 kids ranging from 11 to 4 who are very much into LEGOs.
My two daughters are into the LEGO friends sets, while all three enjoy the various Harry Potter and LotR sets as well ,havent quite got them sold on Star Wars yet:(, but in all cases, they build what the instructions say once, and then we never see that again. It gets broken down, and incorporated with the rest of their LEGOs.
So has LEGO sold out? They still have their original set series and assorted blocks, and options to create your own, and sets for the "billion-dollar franchises"
My kids truly enjoy building worlds with some of their favorite movies, using blocks or characters they can associate, but their creations are still original.
For Christmas this year each of my kids are getting a (small) LEGO set from one franchise or another, and a larger gift of 650 assorted blocks, no sets, no instructions, but we had to go online to get the latter.
I find Toys''R''Us to be less guilty of this, but most stores do not offer the LEGO original sets, or if they do its very small section on the shelves.
As for the kids, well i know mine enjoy LEGOs as they should, but for any kid who cannot do more than follow set instructions, their parents aught to throw away those instructions and teach their kids to enjoy imagination.
In my opinion, if there is any issue, it is in what stores choose to stock on the shelves.