I wouldn't say its impossible, the way Citra Multiplayer works is essentially allowing Local Wi-Fi over the internet and pretty sure I read at one point it should be possible to do on the 3DS just doubt anyone is looking it to.
Would be cool to see 3DS be able to connect to a "Citra Server" which would enable this.
Why don't you just say, "There's a thing now that lets people play wireless Switch games over the Internet."
... But I guess that kind of answers the argument that there's no way the Internet would have sufficiently low latency as to allow local multiplayer 3DS games to be used over the Internet.
That said, no one has made any such software for 3DS games yet. There's been talk of trying to do StreetPass over the Internet, but even though the protocol there has been documented, it's currently too much work for anyone to take on. Local multiplayer would probably be much more complex. (There's not even such a thing for the original DS yet.)
Can't find any threads about this particular issue on GBAtemp or the wider intarwebz. Saw one video on YouTube that seemed relevant, but it was some dude with the same issue, no solutions offered in the comments. :/