I rode through the park shortly after the collision at the end of the Ditchling Devil audax that day and together with others was diverted around the spot by a heavy police presence. It was a sobering end to a great day on the bike and my thoughts are with the injured rider.
Agree with Tim above that Richmond Park is no longer a pleasant place to ride at weekends - this is mainly due to the huge volume of motors, but it has to be said that some groups of club cyclists using the circuit for flat out training contribute to the situation. By definition they will be aiming for a speed above 'evens' and that heightens the risk of collision with so many cars, pottering cyclists and pedestrians about.
I would love to see some restrictions on cars in this park (and in others), but we are a long way from seeing the political will to do that, and past attempts to push the idea have failed miserably.
Perhaps a compromise solution would be to set aside a period each week for more sporting riders to use the circuit road, with cars banned, speed limit relaxed and all park users made aware of this time slot - maybe three hours early on a Sunday morning?
In the short term I expect we will see a burst of police stopping cyclists as well as cars for exceeding 20mph as they will wish to show that 'something is being done'.