Well, sqlite is going to be used for the search feature in Tiger, and it's public domain software (not BSD/GPL licensed, which would mean some restrictions Apple might not like, but completely public domain), with lots & lots of projects using it. The database format and manipulation software are right there.
Sqlite gives you a similar sort of feature set as Access - simple SQL databases in individual files (no server component, just file manipulation); most but not all SQL-97 feature set. That of course doesn't include a GUI - that would be up to others to build.
There are some out there - if you do a google search for "sqlite gui" you can see that they're all currently pretty clunky. But, that's what Apple is great at.
So, if Apple did decide to try to fill out their office suite with a DBMS and spreadsheet, I'm going to guess that the DB side will use sqlite for the file format and manipulation. Which would be very cool, because sqlite really is an excellent database tool - the performance is great, it's pretty mature...