There are already Bitcoin ETFs and other stock-market tradable products in many jurisdictions (not US though). These are very straightforward for casual user, I don't see how it would be any more insecure than buying for example Gold ETF.
Bitcoin (let alone a Bitcoin ETF) doesn't scratch the surface of all of the financial services that can be implemented with Smart Contracts. I agree though that is certainly going to be a piece of the overall landscape. Beyond financial services are things like Smart Trusts.
