Using brokerages that are sufficiently capitalized to clear the trades you want to make. You might have to pay fees to do that. Having other people assume credit risks on your behalf usually costs some money.
The money you put up to buy a stock is your money. SEC rules require that it be kept segregated. It is at no point available for your brokerage to post as collateral for its own risks.
DTCC protects brokerages from each other. Brokerages post collateral to insure each other in case a brokerage fails, and the customers, at other brokerages, on the other sides of the trades from the failed broker, need to be made whole. The clearinghouse isn't insuring against you the customer not being there with the $15 to buy your GME share tomorrow. It's insuring against something horrible happening at Robinhood that zeroes out all its accounts, drives it out of business, traps all its staff in a deep sea diving bell, that kind of thing.
So would instant clearing help with this? If I am able to spend my $15 and the exchange of equity for cash is atomic then this becomes less of a problem?
If you eliminate the credit risk between brokers, you lower the capital requirements for brokerages. But you create other problems. I don't have any opinions about it; I would just form my opinions by reading whatever 'JumpCrisscross says, so I refer you there.
