Option A. Go for it, I say. Maybe we need to form a database team? In addition to PDO support, there's the referential integrity and transactions which David described. Additionally, just general database optimization and configuration recommendations could be described. Killes did a lot of work on making drupal.org work better. While there's room in the PHP code for performance improvements, probably some of the biggest and easiest to obtain are in the database. It'd be nice to have a couple of database layers to choose from, so as to support the widest variety of installations. That is, for example, a layer which supports PHP 4 and MyISAM, for small sites on cheap hosts, to a layer which supports PDO and transactional engines only (no MyISAM) for high-performance sites on high-end hardware.