Now that the first Beta of the coming Joomla 4.1 is out, I have started playing around a bit. One of the advertised highlights is the possibility to create not template copies, but rather child templates (like WP are doing as well as similar to what the folks at Yootheme are preaching).
There's a nifty new button in cassiopeia 'Template Details and Files' that replaces the 'Copy Template' button
It's missing in Joomla 51 templates and I wonder whether there will be any re-working done on those?