I completely agree with "insufficient attention and research has been pointed at" this , and I suspect you're right that "Its a real and significant issue", but I'm wary of using the England WC winning team as evidence without knowing what the rate is in the general population, and what the rate is among other teams of the same era.
Is 5/11 in one team an outlier (like you sometimes get random clusters of cancer cases) or is it the same if you look as closely at any team from the 60s? Is 5/11 especially high for the general population in the same age-group?
The detailed post-mortem brain studies seem to be currently focused on athletes who are expected to have impact-related brain injury - and a lot of of damage is being found - but what do the brains of non-athletes of the same age look like? Or athletes in other sports?
However, as I said in my previous post, asking for more evidence isn't just an attempt to ignore the problem (even though this is a common tactic amongst climate-change deniers and the like) and I support assuming the worst and protecting people (especially kids) until we know what the dangers really are.
Ultimately I don't think I'd miss heading the ball if it was banned. It'd obviously lead to a big change in the way the game's played, just like when the offside and backpass rules came in, but once everyone adjusted, I think you'd see a bigger emphasis on passing, teamwork, and individual skill, which, as City fans, would only be a good thing for us.