It appears that Ryanair's less than random seat allocation policy has been rumbled.
Ryanair admits that it tries to 'keep window and aisle seats free' when randomly allocating seats
I think they are missing a trick here as if they told people that they will probably be allocated a random middle seat it might prompt a few more to fork out for something better.
I actually have no problem with this as I'm happy to pay the small additional amount to have an allocated seat, and given the new rules, to also be sure of getting my carry-on bags carried on.