Wuttt so you mean sky3ds boot as gateway? Or just make gateway usable on 9.7 etc?
On a New 3DS 9.0-9.2, Gateway relies on a bug in Cubic Ninja (or Zelda: OoT) to be able to run its launcher. The Sky3DS is able to run Cubic Ninja to be able to take advantage of that bug to reach the launcher. Once the launcher is reached, you can install things to be able to reach the launcher without Cubic Ninja or Sky3DS. This does not make a Gateway card useable on a system with sysNand past 9.2, unfortunately.
Sky3DS works, to my knowledge, by mimicing the target game as completely as it can. The 3DS cannot see a difference between a physical copy of a game, and a Sky3DS running the game, which is why it's able to still work even on 9.7. The downside of that method is that there's no way to send commands to the card, which is why it has a physical button to cycle through games. Gateway works by running its own code to modify the system, allowing for things like running unsigned code, adding the game menu with Select, emulating a separate copy of your NAND memory, and so on, which is why it can't be used on system versions above 9.2.
In order to be able to be used on 9.7, the Gateway team will have to find a new security hole that will allow them to get into the system internals on that version, which is very difficult and tends to be somewhat luck-based. There's no telling when or if such a hole will be found. If your system version is already past 9.2, you are most likely better off getting a Sky3DS.
As far as the 9.7 support goes for Gateway, that applies to support for emuNand up to 9.7 on Old 3DS. New 3DS still only supports emuNand up to 9.5, and both systems must not have their sysNand above 9.2. sysNand is the system memory physically inside the 3DS, while emuNand is a separate copy that resides on the system's SD card, so it can be updated and used by the Gateway card. That lets you get new features without being forced to move past a system version that can be exploited. sysNand has to stay on a lower version so you can reach the emuNand, since when the system powers on, it starts with sysNand.
I hope this helps explain some of the workings of the cards, and why things are set up the way they are. If you still have any questions, I'd be happy to do my best to answer them.