The idea is to have an simple cache key for documentModels.
This cacheKey will be helpful at least for managing invalidation of page fragment cached with s:cache.
<s:cache key="#{currentDocument.cacheKey}"> ... </s:cache>

For a basic implementation, this cacheKey could be generated with :
documentId + sessionId + timeStamp

documentId = uuid
sessionId = core session id (isolate security problem at least for now)
timeStamp : time stamp of the last write operation in the core

The timeStamp generation could be added to the dublinCore event listener.