Fortunately, it seems nobody broke their systems with the script. If there's no need of improvements, I'll put it on hold as a proof of concept, along with the attempts to the interspersed-track variants. Comments on this are welcome anytime.
For newer testers:
cd ~/tmp wget -O testscript https://pastebin.com/raw/Y2GxuzaY dos2unix testscript chmod a+x testscript less testscript # ---> mind the configurable countdown_step echo ; echo ./testscript -h