To solve 'security' for non-computer people, you'd likely need non-computer wallets (paper wallets...grandparents are already familiar with important documents, or so I read).

For a "user-friendly-version install":
1) Test the user's printer.
2) Load some bootable image onto a flash drive.
3) Restart and boot into the flash drive.
4) Have this pristine world generate and print paper wallets.
5) After it reboots back into mac/windows, (on the paper wallets can be instructions for making the equivalent "watch-only" wallet, and something like *ONLY LET THOSE YOU TRUST SEE OR COPY THIS PART OF THE DOCUMENT* for the private keys).

Obviously the "spend problem" is more complicated...funds could be spent:
Within tiny-Linux again, or via a version of "offline transactions", or you could make every transaction immediately dump the remaining/unspent BTC into the "next" paper wallet...needs lots of wallets and not as user friendly, but good for large transactions.
OR, maybe they NEVER spend the BTC...since banks/lenders can use the blockchain to see how much BTC is in a wallet, normies can just borrow USD against the paper-"savings" BTC wallet as collateral (what Zuckerberg does with his FB shares...tax free!). For smaller transactions this would be ideal. (In fact, a BTC payable credit/debit card would make a month's worth of transactions into one transaction...[for transactions that don't need to be anonymous]).

...clearly it depends, to some extent, on new BTC innovations.