The global lock is something that will always exist with their architecture. It isn't a feature to implement, it's a total redesign and rethinking of the fundamentals. Their much-vaunted in-place, memory-mapped I/O architecture becomes useless because concurrency means using lock-free data structures. MyISAM in MySQL locks the entire table because it does in-place updates. Row locks can't just be added into MyISAM. It'd be such a redesign to add it, it'd end up being something much more like InnoDB than MyISAM. 10gen would have to eat an awful lot of their own words if they decided to go that route.