Non-allocated seating gives passengers an incentive to ensure that they arrive at the gate ontime or early, and it is my experience having handled airlines like easyJet & Ryanair that this is generally the truth
Not sure that I totally agree with this. Yes, it is an incentive, but in my experience the stragglers that turn up at the end, aren't really the type of people that will go rushing to the gate at the thought of having a good seat.
I've boarded both seated, and non-seated flights. And my view on the subject is that allocated seating is quicker, more efficient, and much more passenger friendly. Having said this, staff have to be properly trained. There's no point allocating seats, if you've then got to do 20 seat changes at the gate because of a hash up at check-in.
At least a trial wouldn't go a miss. Easyjet own their own reservation system, so it's not going to cost them $$$$$ to have the changes implemented, even for just a trial!