It was said that it's really easy to block, in just a couple lines of code.
Because Sky3DS isn't full 1:1 emulation of cartridge communication they would just have to add a check for something the Sky3DS doesn't emulate correctly.
They could make it have 1:1 emulation if needed though, but it appears they will just put out new hardware revisions for incremental fixes and simultaneously fuck their existing user base in the ass, so don't expect perfect 1:1 emulation for the next few hardware revisions (in other words, several hundred bucks could go down the drain before that finally happens)
It's not an exploit per se but it's imperfect so Nintendo could very well release a patch within the next day that blocks Sky3DS if they put in the effort. They may not have a Sky3DS cart on hand yet to analyze how it works but i expect it won't be long before they block it.
If they are determined, which it shows, than indeed I'm expecting a sky3ds blackout in the coming month. If GW is releasing there 9.2 update on 12/25 it would be parents rushing to get there cards updated, tested, and with games and tears in kids eyes and teenagers ditching there so called 'love of there life' to be using there update at last, parents actually having some time alone in the bedrooms while kids hammering away at there 3ds.