I already have a 3ds xl with gateway are there any advantages having a new 3ds with gateway than a old 3ds?
If you get a Sky and the N3DS FW is <= 9.2, said Sky can act as the Cubic Ninja to launch GW for EmuNAND (or other homebrew).
You could also get a normal copy of CN.
Of course, CN exploits and Gateway won't work above 9.2 while Sky's normal ROM prowess will. Depends on what you want to do.
Edit: Advantages... aside from N3DS games which either Sky or GW can launch, none in particular thus far. The O3DS currently wins in that it can run 4.5 and EmuNAND up to 9.6 without a GW (though I believe a 9.6 EmuNAND can't run CIAs currently)