Most likely 10.3. It takes time to assemble the N3DSXL so it's unlikely it will be 10.4 but you never know.
As for if it's worth getting. That's up to you. If you're a fan of Fire Emblem and were already looking to buy a N3DSXL then I'd say go for it.
Go with Sky+. Like others have said, CN can easily be added to the blacklist and patched so your purchase would pretty much be useless if they do so. At least with Sky+ it opens up other functionality as well as having the ability to have CN. It's not that much more anyways.
Super Smash Bros also changes the language based on the console language. It's mostly with first-party Nintendo games that do this that have been localized and released all at once.
Most games shouldn't have this problem but there really isn't any type of workaround other than playing it on a US...
Tried it using with a Sky3DS version of Cubic Ninja on 9.7.0-25J and it just crashes the game and restarts the system.
EDIT: Woops, forgot to set it to 'NEW'. Anyways, awesome work with the exploit. Didn't think it would happen but it did!