The Sky3DS is a ticking time bomb. It will become useless the moment Nintendo releases an update that blocks it. Unlike Gateway, there is no way to update the cartridge once an update blocks it and it can't run homebrew (well it can via Cubic Ninja exploit, but not if your on firmware 9.3 or above!) or make use of Emunand or firmware spoofing. Hell it can't even undo region lock.
Useless unless you, well... don't upgrade? Sure, you lose access to eShop and future games that are built on a higher firmware, but you still have access to the entire library of 3DS retail games. GW offers way more functionality, has a better promise of a future, and is cheaper but useless is quite the overstatement.
I'd expect some Sky3DS users to agree with me, but most of them are probably off playing their games in bliss and not mashing F5 on this thread.