Attempting to access kosto.shoutwiki.com results in a 503 error.
This is somewhat "intentional" for the time being.
After we rolled out MW 1.27 (see T90: Upgrade MediaWiki to 1.28 and the blog post about it on our blog) and turned out that for the first time in our history, we had to roll back a major version upgrade, so we started wondering how to debug this issue which had not popped up during our testing. I suggested implementing our own version of heterogeneous deployment (because the WMF's code is highly specific to their environment), which I've implemented in our LocalSettings.php. The idea was simple: if the subdomain is in a predefined list of "staging" wikis, use a different (1.27) MW codebase than for the rest of the sites. This would allow us to try out things with the new codebase and see where the problem lies without breaking any live, actively used wikis.
Of course it's not that easy when we're talking about MediaWiki. What you see as a HTTP 503 is actually a bunch of weird PHP errors that make no sense as something doesn't quite work the way I envisioned it. As for why this is still happening: we're still working on MW 1.27, obviously, and reverting that staging area stuff wasn't a high-priority task because it literally affects one wiki which isn't exactly our most popular site (trust me, I know, as it's a wiki I started and I'm like its only editor so far :-).