So, I thought about this a bit... I think arch would benefit greatly from having a defined set of "package types". It should be fairly open-ended, but would remove alot of repetative code.

for instance:
pkgtype=module would run depmod -ae upon install
pkgtype=scrollkeeper would run the whole mess of scrollkeeper updates
pkgtype=fonts would update all the needed font stuff

these types should reference scripts to do the duties... to make everything concise, I'd say including the scripts in the package would be a good idea (that is, only the packager needs the scripts locally)

with something like this, it would be fairly easy to only upgrade the kernel when all pkgtype=module packages are likewise updated

I could see a feature like this being a very good step for pacman (and packagers), however, it may be complicated to implement