The way debian handles this:
- standard licenses are in /usr/share/common-licenses, these licenses are just like our licenses package
- every package contains a "copyright" file in /usr/share/doc/pkgname, this file contains information about where the sources are from, a small version of the license, and a hint to view the complete license in /usr/share/common-licenses

Our policy for documentation is a bit weird at this moment. Take a look in /usr/share/doc -> you'll find directories named after the package name, directories with capitals in it, directories with versions, etc. Another thing is the name of the copyright file in /usr/share/licenses/$pkgname. If we want to change this, we should take some steps:
- make sure /usr/share/doc/anything is named after the package name
- install or symlink licenses as /usr/share/doc/pkgname/copyright or COPYING
- packages that are not a generic license type, like GPL with exceptions, require a COPYING/copyright file with the name of the license, the exception below that and a reference where to read the rest of the license

Heres how Slackware handles this and IMO the safest & better way:

mkdir -p $PKG/usr/doc/apmd-$VERSION
cp -a \
AUTHORS COPYING LSM README apmlib.COPYING apmsleep.README \
$PKG/usr/doc/apmd-$VERSION
cp -a xbattery/README $PKG/usr/doc/apmd-$VERSION/README.xbattery

That means treat every license as uncommon. You can copy over examples and other stuff you find useful in /usr/share/doc/$pkgname-$pkgver/ for the end user like apmd above.
That also means less automation in PKGBUILDs.
But even for example if a license changes, you are sure you are distributing the package with the correct license.
Now that im analysing this im not even sure if the license array if even needed in that case but i wont go that far.

The last sentence is kind of confusing. I mean the license array in PKGBUILDs.

I like Jan's idea better, but it's a lot of work to do the symlink deal.
Perhaps some post_install magic to check to see if the copyright file exists, if not then symlink the file from the licenses array.

May i ask what does "- simplify doc building process for ease of development" means from the pacman 3.2.2 NEWS?
Is it in any way related to this?

@Dolby: not the place to ask and not at all.

Since, this isnt high priority, quite the contrary, its better to wait as much as needed, and implement the documentation incl. licenses, as the developers feel it should impemented properly. Perferably not handled by $pkgname.install.
I dont know if you wish to keep this open as a reminder, or close it, as the request has been denied.

I don't know what to take out of this bug report (crawling all things assigned to me tonight). Can I close it since I don't really know what to do or want to make a overarching policy decision on this?

I'd say feel free to close. We use the /usr/share/licenses folder for licenses and "common" licenses are obviously common so packaging them separately makes sense to me.