FWIW, they are charging to pre-book seats from the time of booking until 24 hours prior to departure. i.e. the option to pre-select the remaining seats for free within the 24 hour period is still available.
So families who want blocks of seats together should still be able to do this for free, it will just be the more lucrative exit row seats etc that will most likely be "purchased". Just wanted to add some balance as this fact seems to be little reported.
Pre3