It would be useful for me to write something like this in a topic: <para>This topic was last updated on <!--insert.lastedited-->. Things have probably changed since then, so your mileage may vary!</para> and to have the builder inject the date of the last update to the topic.
This isn't a CSProcessor issue. Injections are a Skynet based issue so I'll move it over to that queue and I'll have to discuss it with Matt. This is a Skynet issue as you can't have custom injections for the CSP and not be supported or ignored by Skynet without adding any code.