After seeing BruXy's BASH on fire page (http://bruxy.regnet.cz/web/linux/EN/bash-on-fire/), I thought (yet again) "I can do that better in awk!" and started writing :-)
Half an hour or so later I had my first working version and here it is. It could definitely use quite some improvements and features that I have in mind, but that's for later.
On a quiet evening some 4 years later, here's a slight improvement on the effect. More colors and a bit better resolution.
Here's an image of the result:
awk-fire8-sml.mp4
For a better version see: https://youtu.be/IzCu6BYeI4o