I would personally not buy GW on empty promises, only if you can use it for something it currently actually does. There really shouldn't be a need for another card for N3DS support, since GW is really nothing more than a softmod, but I wouldn't put it past them to try to scam existing customers out of more money by requiring a new card. There is no honor among thieves, as they say
That said, I am hopeful the update will work fully with the original card and will be out soon, but no one has any idea because they would rather ignore their customers.
As for your specific problem, since you have two machines that both currently only work with Sky, you would obviously need 2 of them to play at the same time. I think the cheapest solution would not be getting another Sky card, but getting another 3DS that is 9.2 or lower, downgrading it, and installing CFW, and selling your 9.4.