The "nostalgia" routes still ocassionally operated by Routemasters (I use the 15 infrequently) are a fantastic study in why open platforms work so well.
They quite often catch up with the more modern designs because of the speed in which passengers get on and off. Plus you can decide to abandon ship if the traffic is exceptionally heavy to walk instead.
And as a Brucie bonus, it's often amusing to see tourists run after them when they accelerate away.
I am a regular user of the 15 and can attest to this: especially during the evening peak on the section east of Aldwych, it's often a little quicker to wait a couple of minutes for a RM, because it'll usually overtake a couple of regular 15s en-route. Plus, there are usually more seats available (with the exception of the middle of the day on weekends, because they're always packed with tourists who try and pay the clippie as soon as they get on.)
Of course, whether or not this speed will be matched with the Borismaster remains to be seen: the front and middle doors will still need to be opened (by the driver) and then closed, and the second crew member will need (presumably) to give the driver two bells before she's allowed to set off.
If there was an enforced (or even de facto) policy of "exit via the rear door wherever possible", this problem could be obviated a little: if you have an open platform, alighting passengers can safely queue to get off, and then hop off the very second that the bus is moving at a safe speed (before it's even stopped, usually.) This is better than current double-deckers, where most passengers remain in their seat and then have to barge their way through a dozen or so standing passengers after the doors have opened.
For passenger flows, I'd say the Borismaster is built on very sensible principles, but we'll need to wait for it to arrive in London and work a few 38s in the peak hour to see if it's worth it in practice.
Of course, I doubt this will have any major effect on the future of the bus: if Ken is elected, he'll consign the prototypes to the LTM as a symbol of a previous administration; if Boris retains his position, he'll plough gleefully onwards, and by 2015 there will be armies of scarlet-coloured humming Milk Trays on London's streets, for better or for worse.