Apparently the new AD is in response to an in-flight wing spar fracture in a Cap 10b in June this year. It happened in the USA, and according to my source, the aircraft was licenced to fly in the 'experimental' category. This Cap 10b was one of the older ones, and it is suspected that the spar fracture may have been the cumulative result of excessive G over many years.
However, until the incident is fully investigated, Cap 10b's are to be placarded to +5/-3 solo (less with two up) - hopefully temporarily.
As pointed out before, the Cap 10b is a very slippery aircraft, and in any kind of downline it can be easy to build up speed, which may result in excessive G being pulled.
Its very worrying to think, that in multi-user aerobatic aircraft, ie in group or solo training situations, that some people may inadvertently pull excessive G, and it goes unreported. Then, months, perhaps years later, their stupidity results in someone getting killed. Thats why I don't let anyone else fly aeros in my plane, unless I'm there with them.