A further (very crude) idea I have also considered is if EOS and ETH can be linked in some way, such at individuals can opt in for further security where one of the multi-sig accounts is provided by an ETH private key.
Periodic "backups" of fund numbers on the EOS blockchain can be made on the ETH blockchain (with gas paid for with ETH of course); and for funds to be transferred beyond a certain limit out of this account/contract, the ledger on the ETH blockchain need to be updated first to enable the actual transfer on the EOS blockchain to go forth. i.e. If there are 500 EOS tokens secured and the amount updated on the ETH blockchain, and the threshold is set of 10%, then only 50 EOS tokens can be moved unless the ETH ledger is updated or the threshold is modified.
This allow the security level necessary for institutional level of custodians trying to operate on the EOS platform, while also keeping the large sort of funds on the EOS platform w/o having to trade them for something else that they might deem more secure (in terms of centralisation-risks).
Perhaps, alt-chain linking can be further expanded to include say Cardano (once their smart contract layer is up), or Nano, and so on.