[PeterisP]

Payment delay has only a little bit to do with infrastructure and a lot with competition and incentives.

If you're required to do, say, next-business-day payments but your infrastructure gets them done in 5 minutes, you could still want to delay all those payments to the next day since there it makes a significant addition to your revenue (float of the money held, interest on overdue customers, payment fees for 'more-urgent' payments) - unless competition forces you to do so.

Banks aren't sitting on their hands - you should expect a "transfer system that works" from banks as soon as someone actually threatens to outcompete them. Square Cash doesn't seem to be that thing - it relies on banks allowing the debit-card-refunds (AFAIK they are allowed to kill this ability as soon as they wish to), and I'm sure the banks make sure they earn 'their due' in fees on every such payment anyway.