variables for tables and columns?

Would it be a lot of trouble to extend the ability that databases have
to store variables (add_missing_from, array_nulls, etc.) to tables and
columns, for use with user-defined variables?

This would make it cleaner, I think, to do things like automatically
build UIs for a table, using the variables to configure exceptions and
special features, especially when using mod_libpq or otherwise trying
to minimize the code that exists outside the database server.

What do you think?

Thanks,
Kev