Twice this week I ran into a situation where my speakers were overheating. In my case, the speakers I am using are sound exciters, so they are not enclosed - they are in the open, where they can easily come in contact with anything nearby, including my skin. I would liken the temperature to an iron on warm. It's not fun, and I found out via google that the since removing PulseAudio - Alsa sends current to the speakers while paused. With nothing to play, and just a flow of current, the end result is massive heat buildup.
My setup: Raspbian Stretch lite on a PiZero Wireless, headless, with a Pimoroni Phat Beat configured to run VLC radio. Power Supply is adequate at 5v and 2 amps, and when not paused, there are no heat issues, even when running volume pretty loud. As soon as the pause button is enabled, or if VLC radio decides to cut out on it's own, (my second instance), the heat buildup occurs. I will test with mopidy.
Someone at Pimoroni is already looking at this (believe his moniker is Gadgetoid), but I see this as a serious issue with ALSA and the latest version of Stretch/Lite. You definitely do not want to use sound exciters as speakers with ALSA.