So it's a centralized `pv` ?
It would be nice for cp and mv to just have built-in progress bars (only active in interactive mode, etc).
Here's the POC if anyone would like to take it further: http://anthias.sourceforge.net/
tar c -C /tmp/source . | pv | tar x -C /tmp/dest
you can also pass an approximated size of your source to pv, however the tar output will be slightly bigger.
A bit clumsy, but it shouldn't be hard to write a little script to do it.
Anyway, if cp -R had a progress bar it would behave the same way, i.e. it would have first to recursively stat the source the same way as du does, and only then it could start reporting a completion percentage.