Nima,
In theory, you're correct - all you have to do is add some XQL files to CVS to support a new db.
In practice, however, there are more than a few lines of database-specific code in OpenACS that would have to be refactored. You would also have to update docs to deal with installing the proper db driver (odbc or native). Then of course after you did all this (mucking with code that 100% of the community relies on to service that 0.001 %) you would have to commit to maintaining the code+docs+tests going forward. And even then you would not have started to port the huge library of package-specific sql code or address coordinating this with package maintainers.
If a project of this magnitude were to be taken on (which is highly unlikely), it would be better to support the other 99.5% of web servers (with something like portable.nsd) rather than a database with ~30% market share which very few folks with OpenACS expertise care about.
