I sent this mail to them:
And they responded:
What do they mean the current gateway is compatible with my 2ds? If I get a gateway today I'll be able to play backups on my 2DS on the spot?
Maybe they didn't understand the question, but I already bought a GW from yeahgeek, so let's wait and see in a couple of months if it will work/update on my 2ds.
They already stated in an email, that you don't need another 4.5 device to update the gateway. So you will be able to update the gateways on the market yourself, we simply don't know how.