It will never be 100% solved due to CAP theorem. There will always be a window of time where it could be applied, even if its short.
With our consensus and ledger, a double spend is very difficult to do due to the logistics of catching the available window, and the costs associated with being in a position to actually influence one. But, its still possible, just highly unlikely.
I'm not an expert by the language of John's Whitepaper he seems to think he has solved it.....not just made the likelihood of it happening negligible.
Are you saying John is wrong or that he never really technically said its '100% solved'