Are FKs handled by core or InnoDB
I don't know the architecture of MySQL, but by reading a bit on the forums and MySQL forge, it seems that foreign keys aren't currently handled by MySQL, but by InnoDB engine directly. I think this will change sometime in 6.x.
Is this still the case for Drizzle or are you re-engineering this? If yes, does this mean other storage engines will also support FKs? If no, what is the likelihood that you'll port this (or other things, for that matter) back from MySQL, once it's done there?