This is all very interesting. I would have loved the opportunity to do some of my written exams at GCSE on computer, like History and English. I can write at an average speed, but in exam pressure, it's difficult to write at that speed and write without making mistakes, which means crossing out quite frequently.
My only concern with having computers for more people/everyone is that there is huge variance in typing speeds, whereas writing speeds are fairly similar for everyone. I can type at around 115 WPM, and I think the average is around 65WPM, so people who are more-experienced typists and who can touch-type etc. could have an advantage.
However, I suppose if examiners don't change their marking methods, this would be fine, because most people who work hard get the grades they deserve, and only a few miss out on the top grades because of exam pressures or disadvantages because of writing difficulties.