Currently, there is no page_content_format field, and "Each row in the content_model table will refer to a unique tuple of (content_model, content_format)." If a page's content model allows multiple formats, which model ID would be used? Perhaps there should be separate content_model and content_format tables.
Topic on Talk:Requests for comment/Content model storage
Yeah, that's a good idea. I talked with @Duesentrieb briefly and he liked the idea of having two tables. Will update the RfC shortly.
Separate content_model and content_format tables are much better, thanks.
Perhaps it would also be useful to put the default format for each model into the content_model table, as cm_default_format. This would be useful during migration, for filling in NULL values in fields like rev_content_format.
Maybe I'm misunderstanding what you meant, but wouldn't we fill in NULL with whatever ContentHandler::getDefaultFormat() returns? Why does it need to be in the database table?
Having it in the database would allow us to fill in the blanks without leaving the database. It's an option to consider, which may come in handy for some use cases. But you may very well be right that we don't need it.
I would rather keep it in PHP, mostly because you already need PHP code to "fill in the blanks" for things like namespace names. In any case, I'd like to leave it out for now because I don't think we should have the default specified in two places (PHP and database). Plus one of the goals of this RfC is to make changing the defaults easier, and this would somewhat work against that.