> 2. Require preparation functions to accept one parameter, the project
>    plist.

I think adding project-plist as a parameter to preparation functions is
definitely more elegant.

But, I also came across this old thread where it was noted that making
project-plist a proper parameter, instead of it being dynamically scoped
into the preparation function, would break a lot of code.

https://lists.gnu.org/archive/html/emacs-orgmode/2010-03/msg00016.html

But now, with org moving to lexical binding, I think it is time to make
project-plist a proper parameter, despite the costs of doing so.