I've noticed that the MLOCK modes are hardcoded, based on IRCd. I've also noticed that many custom modules for some of the IRCd's add modes that Anope is now unable to MLOCK. I've also noticed that it's been requested in a few ways, just not here. And mostly for 1.7, I think..
So my suggestion/request, whether by module or by core, is to have the standard modes per IRCd defined, but additionally be able to add the mode letters/flags for the custom modes in config.
And I understand that it will likely have to wait till 1.9. I have patience ;-)