Hmmm I surely disagree with the response from Pentax. It is as simple as a firmware upgrade and it doesn't require any more processing power.
The shutter speed during filming is a variable controlled by a lighting meter and can be locked with ae-l. So how hard can it be to control that variable with the front wheel? I think it's even possible while filming. And when the light meter is disabled (because of the manual mode) the processor uses less processing power.
So what are the costs for Pentax for this, hmmm at max 1 day of programming (by a single programmer), and some testing. So that's not that much. The reason that Pentax doesn't implement this, is just marketing. They might implement this on a future model, so then there's a reason for us to buy the next model
A small note; I am a programmer so I know what I am talking about