Earlier quoted context omitted.
Wasn't a big part of this issue fueled by RH fronting the money for trades when the customer was transferring money into their account from a bank over ACH? Making ACH instant (which I believe is in the works) would solve that, not T+0 for settlement. (I don't have a good feel for what was the bigger driver of RH's issues though: overextension because of slow ACH or slow trade settlement.)
No, that was negligible. Robinhood actually fronts the least money out of all major brokers (something like $1000). And if that was the case the easy solution would be to block trades if your account didn't have the sufficient settled balance.
None of the brokers I have ever used have ever fronted me money. If the required equity isn't going to be in the account by the settlement date, they won't spot me so much as a fiver.
There's an argument to be made that Robinhood Instant is a violation of federal margin regulations because it allows margin risk to be taken in an account with no settled equity.