The three main functions the web interface needs to provide are:

• Now playing
• Chat
• Voting or similar two-way interaction with mpd

Originally HTML and some form of CGI seemed like the way to go. This is an offline hack and not a hardened, web-scale app, right? Well, in the last few days of research and noodling in VMs, I'm increasingly leaning toward a Node.js stack. The speed at which I went from...

npm init

...to a live chat app was a revelation. No lengthy server config files, no permissions jungle to navigate, just a few lines of javascript. Seems to do chat really easily, too.