A couple of simple options to parse sitemap.xml to warm the cache or for other actions such as generating memory_profiler checks.

cache-warmer-3.sh

# This can be added to your cron job to run right after Drupal's cron or combine them into a single command so 
# that it automatically executes when the cron run completes.
wget -q http://www.example.com/sitemap.xml -O - | egrep -o "http://www\.example\.com[^<]+" | wget -q -i - -O /dev/null --wait 1

cache-warmer.sh

#!/bin/bash
DOMAIN='example.com'

# One liner with wget. This can be used on the cli, just replace $DOMAIN with the domain directly.
wget -q http://$DOMAIN/sitemap.xml --no-cache -O - | egrep -o "http://$DOMAIN[^<]+" | wget --spider -i - --wait 1

cache-warmer2.sh

#!/bin/bash
DOMAIN='www.example.com'

# wget and cURL

wget -q http://$DOMAIN/sitemap.xml --no-cache -O - | egrep -o "http://$DOMAIN[^<]+" | while read line;
do
  time curl -A 'Cache Warmer' -s -L $line > /dev/null 2>&1
  echo $line
done

# If you have multiple languages add another, e.g. http://$DOMAIN/es/sitemap.xml

Inspired by your gist I created: https://gist.github.com/JPustkuchen/f185bee60c5a36211cdf6f1c8f6deebe
Of course the best would be to add an if that checks if the second level only contains sub-sitemap-pages and then jumps into the loop. But I always needed sub-sitemaps so far.

very good, thank you ! :)