Facet system

Are you going to implements a facet system or only the possibility to choose more than one cat?
An example: a reviews blog
A facet system is a system in which you can categorize an entry under semantic
(about php, about sql, etc) and under other kind of categories as kind of resource
(book, site, script, and so on).
A similar system is already used to categorize a post under author, date, category anc so on.
I would like the possibility to add other facets.
Is it possible to know in which release the feature planned is to be released ?
Thanks