Quoting Ivan Sergio Borgonovo mail@webthatworks.it:
And unless support for MyISAM and sqlite is going to be dropped, and I don't think right now is a good choice, using more "advanced" DB features in core would be a double pain.
I don't know about sqlite but MyISAM would continue to work even if we code for the transactional update. It would just lock tables instead of rows and the cascading would not occur. If warned it would be up to the user to make a determination to continue with MyISAM or move to a new provider.
-- Earnie http://r-feed.com Make a Drupal difference and review core patches.