I don’t think you need to go overboard here, and you shouldn’t if you’re of modest means — just hunker down with CPF and CPF LIFE in that event. But for moderate and greater wealth, a little custodial diversification has merit. As it happens, certain offshore broker custodians are much less expensive (in part because of scale and efficiency), and that’s useful, too.
Also, apply some common sense. Practically every developed country offers reasonable custody, but I would not be inclined to hold much wealth in anything domiciled in Venezuela even if I planned to retire there. For example.