I wanted to ensure that wouldn't be a problem on sites built with Midgard CMS and MidCOM. On an IRC discussion with Torben Nehmer, I pointed him to Alexander Alapite's Conditional GET support library for PHP.
However, it looks like this is not an issue, as MidCOM already supports conditional GET if its server-side caching system is enabled:
torben: bergie: the midcom cache does include last modified and expires headers by default, so http head requests in a cached system already work fine with browser caches
torben: at least with nathan-syntronics.de i have a greatly reduced bandwith through this
torben: bergie: apart from that i would wait with further stuff until mrfc 6 has been implemented (or rejected), now that you are here, we can actually start discussing it again
MidCOM's caching engine can be enabled in the "MidCOM Site Settings" interface in the MidCOM site template (midcom-template).
In addition to providing the correct expiry headers, the NGO Geeks provided Midgard Caching Headers patch to the original "Simple Dynamic Site" template that have since been included to midcom-template.
Here is the settings interface:
It would be nice to get some actual testing figures on how well the current HTTP Conditional GET code in MidCOM works.