I used to use it before. Until youtube was updated. Then i laid off my 3ds for a while until I discovered cfw. But im sure it was patched at the time.
Again, it's not an exploit, and again, I use it myself, every single day. There is nothing to patch. Nintendo or YouTube(Google) can't do anything about it.
You'd have to understand what DNS and how it works for me to explain it to you properly. To put it simply, the DNS server is what allows the device to translate a named address like "example.com" to an ip address like "22.214.171.124". What TubeHax does is simply make all known Nintendo URLs redirect to nothing (probably something like 127.0.0.1). As DNS is the only way of retrieving the IPs required for a connection to Nintendo, it will always fail. Nothing short of Nintendo removing or limiting your ability to modify the DNS servers will change that (and even then, people would just block via their home router or something similar).
Edit: I feel like I should note that hardcoding the IPs probably is technically an option for Nintendo. It wouldn't be convenient as I'm assuming most of the addresses are actually round-robins and/or select servers that perform better depending on the user's location. Nintendo could devise a scheme that downloads
IP lists, that could be a bit annoying to circumvent (without CFW), but it's probably more trouble than it's worth.