There is no need to rebuild calibre on each release.
I run from a source install, and all I do is `git pull --rebase` and calibre is updated.
Occasionally, whenever there are changes to the C++ code (uncommon), I do `git pull --rebase && python2 setup.py build`, which finishes pretty fast (faster than the time it takes to download an installer, certainly). So I have to rebuild then. Of course, "rebuild" is not strictly accurate, since since only updated code needs to be rebuilt, not the entire codebase.
But I am on linux, which is the only platform where calibre supports source installs.
You can of course use the pre-built releases, in which case you
must download & run the latest installer, but
your source checkout will override the python code only.
Really, it can all be scripted.
So even if it was necessary to rebuild calibre (which it
isn't) it still wouldn't take any of
your time.
Note: I am not saying anything about the relative viability or fun of using a plugin.
I am merely saying that running calibre from a customized source is much easier than you imply.
re: perl -- I haven't heard that perl is old-fashioned. It seems to be quite popular and active.