We seem to have this issue whenever we want something new associated
with a link: frequency of update, type information, etc.
When you put it in the linkee, do you put it in the transfer method
(extend HTTP) or do you put it in the transferred data (extend HTML).
We had this issue for datatypes, and wound up putting type information
in the transfer method (extend HTTP to handle types).
Part of the problem is that we want to support more kinds of transfer
methods (gopher: and ftp: as well as http:) and also more kinds of
transfer data (.gif and .au as well as .html).
As for update information, I personally think that update information
makes sense in the linkee data. To deal with more kinds of things than
.html, put .gif and .au in some kind of wrapper.