I mean you can still offer credit in T+0 settlements but the real challenge (I think) is setting up an industry-standard margin pledge facility for trades to ha

I mean you can still offer credit in T+0 settlements but the real challenge (I think) is setting up an industry-standard margin pledge facility for trades to happen without immediate availability of liquidity. Here's DTC's whitepaper from 2018 discussing some issues with real-time gross settlement: https://www.dtcc.com/~/media/Files/downloads/Thought-leadership/modernizing-the-u-s-equity-markets-post-trade-infrastructure.pdf https://www.dtcc.com/~/media/Files/downloads/Thought-leaders... TL;DR: Market makers using a netting mechanism to settle trades at the end of the day, and they often don't have the funds necessary to settle trades in real-time.