In case you were afraid to deduce it from the screen I posted, yes, the hack works up to 5.5.1. However, I strongly recommend everyone to start blocking updates. That's why I announced I was working on IOSU in the first place, to raise awareness.
I reached IOSU in 5.5.1 using a different bug (another lame UAF in WebKit) than yellows8's, but the libstagefright one is much more reliable and it's already public. Which means that the release for 5.5.1 will be using yellows8's exploit while I keep the crappy one I used private.
Beware that Nintendo will likely push a big update to the Internet Browser anytime soon (I believe it's logical to deduce that), which will quite likely patch (properly) both the libstagefright bugs and other previously unpatched WebKit bugs (the one I mentioned included).
Marionumber1 also made a solid point about investigating userland bugs in areas not related to the browser (like Mii data, for example), which is something we will likely investigate soon.
Aside from all that, the exploit just needs obfuscation to be released. Like I stated before, the obfuscation layers will be complex which will take time to implement properly. If any delays follow, they will be strictly related to the obfuscation of the exploit.
Also, I mentioned that my "vacations" are extended to the end of February, but that doesn't mean the exploit will only be released by then. I'm guessing it will be done quite before that, but right now it's just a matter of getting it right so Nintendo won't patch it as soon as it comes out.