I have been a passenger on many free seating flights among Europe's low cost airlines. No matter how hard they try (priority boarding for low seq numbers etc) there is always that final crush at the gate to get on first. Indeed I wonder how many injuries have been caused by people running down the aircraft cabin as people boarding from the front and rear both head for the overwing exit rows. It'll be just the same here.
And there seems (to the untrained eye) to be little difference in terms of aircraft turnarounds with those LCCs who do allocate seating.
In fact the best boarding system I have expereinced was a LH 747-400 flight from Frankfurt where boarding wasn't by row number but by letter. Eg: allocated window seats first and aisles last - so no people clambering out of seats to let others in etc.