Shut-offs and pilot's attitude:
A big difference between my test this year of this mechanical system and a mandatory shut-off is the intention of the persons involved. For my mechanics and me it was a goal to demonstrate that the system was working. Pilots that are forced to use a shut-off system will not have this positive attitude to the problem. Combat pilots primarily want to fly combat and win competitions. With this mechanical shut-off system it would be very easy for them to block the function and minimize the risk of the shut-off to spoil the fun. The risk of being exposed with a blocked shut-off is probably much lower than the risk of a competition being spoiled by a malfunction in the shut-off system.

At a competition earlier this year a pilot had a very direct comment on the mandatory shut-off: "First thing to do is to make sure that the dammed thing doesn't work!" I think he had a good point here. If the shut-off is made mandatory before we have a robust an easy to use system most pilots will probably just block it and take the risk of a DQ if they are exposed.
When the muffler rules were introduced it also caused a lot of problems but everybody could see that the noise was a problem. Today it is much harder for pilots to see that the reduced risk a shut-off will give is enough to justify the hard work of building and using them.

The situation now:
Through the last year I have only seen two systems being used in competitions: The Czech system and my mechanical system. In the US Jeffrey Rein have used and sold the H&R shut-off for some years. I have not seen or heard of any more advanced systems with remote control systems.
We are still far away from a situation where we have a shut-off design that can be introduced as a mandatory system. Before we can make the shut-off mandatory we must see a simple and reliable system being tested in competitions for at least a year. If shut-offs are introduced too early we may end up in a situation with unstable systems and pilots trying to block these systems. A situation that only gives pilots a lot of extra work and the security will not be any better than today.
Today combat is highly based on RTF-models, off-the-shelf engines and ready-made propellers. If the mandatory shut-off system shall be widely accepted I think it will necessary with a "Ready-To-Fly" shut-off system.

What to do now:
We have to postpone the mandatory shot-off system a year or two to give time for the development of better systems. These new systems must demonstrate their reliability in competitions for a year and they must be made available for all pilots.
I think that the number of fly-aways still can be reduced further by an increased marshalling of existing rules. We also need new rules that can change the dangerous flying styles we still see by some pilots and in extreme situations.