Right now there is no way to attach information to an article without lozing it over time (like "page_props" table does)
By having a revisionized / versioned properties table (like page_props) many (if not, all) of the following will be possible:
- Store page protection settings with the revision, undoing/rollbacking will bring back protection info. As will deletion/undeletion
- Move categories out of of wikitext. It has been proposed to do this before (ie. store only in categorylinks and report changes in a null-revision edit summary, like with protection currently) - however that is prone to abuse since undoing a revision would mean having to manually copy/paste categories from the history page edit summaries.
- Maybe move langlinks out of wikitext ?
- File properties 
- Custom data for exentions (the prop_type column can be used by extension to store other information, that would otherwise have to be stored in a new-table. Some extensions appear to be doing this currently which could cause many tables for the same purpose on a single wiki).
Using a versioned properties table will solve these problems. The revision is connected to a set of properties, and undoing the revision will re-use the previous set of properties (just like a rollback re-uses the same mw_text.oldid_id / mw_revision.rev_id)
It also saves storage in the database as the set is only re-saved when something has actually changed.
In other words, if the user only made a change in the article text, the same old propid is used. If only props are modifed, the same textid/oldid stays in use.
The properties table would have it's sets identified by a unique id, stored in a column in the mw_revision table . The properties table would either be it's own incrementing integer or use the revision id. Comparison:
- Since multiple rows belong together the id spans multiple rows. An incrental ID that spans multiple rows is not supported in MySQL and the only solution I can think of is either keeping track of the id elsewhere, or getting the last row and using the next number. Both are not clean.
- Using the revision-id is a lot easier. The revision data is saved, the revision-id is known and used to store the properties. This also makes it easy to track which revision last modified the properties (since the id matches the revision-id that created the set of properties).
I think using the revision-id is probably the better choise. Only down side could be that it may cause confusion since it would look like the revision-id, not sure if that's an issue.
- Store data in properties table, versioned and each set has it's own id. If only props change, same text.oldid is used, if only text changes same propid is used.
- Connected revision to a set of properties, like text id (ie. a rollback re-uses the oldid that revision, same would be for properties. Rolling back an edit creates a null-revision with the same old text id and properties id.
 Adding a column to mw_revision is expensive to say the least but I'm not sure there's a clean and long-term effient way around it.
 bug 25624 and http://www.mediawiki.org/wiki/License_integration
- (bug 167) Use a dedicated interface for adding interwiki/category links, not wikitext
- (bug 25624) Making license and author information api accessible
- (bug 835) Syntax to transclude a page without categories and langlinks
- (bug 22293) Show previous protection level in protection log