To be fair, if he hadn't been IMC while under SVFR/ VFR, he probably would have seen the crane and hopefully avoided it.
He sounds like a nice guy from what I've read but he broke rules and it killed him. The rules exist as a result of many accidents over the years. They get refined when things happen. For me, there are no extra take aways from someone breaking the rules which were put in place to help him. He broke them, he died. Sad yes but true.
Marking cranes would not have helped this crash as he was supposed to be VFR anyway (key point being 'visual'). What can the CAA realistically do, approve cranes during housing development? Lets be clear here, over London, people should expect cranes, tall buildings and other aircraft, this isn't remote northern Scotland, it's the capital.