Pretty disappointing news.
But it shouldn't be hard for Nintendo to block. I know people reference how you can still use DS flash carts on the 3DS, but that is more because the 3DS is emulating a DS when it runs those, so it is harder to fix security flaws.
As it is, it doesn't break the region lock. It doesn't allow multiple games per flash cart. It doesn't allow homebrew. So even the people who go on about legitimate use for flash carts would have no legitimate use for this.
Also why do people complain about eShop prices for digital games? I don't know about the American or European eShops, but the Japanese one has sales time to time, and reduces prices permanently on some titles.