This video shows MSI's B650M Project Zero motherboard, which aims to move the motherboard cables to the back of the board. It's not technically a 'form factor' yet, but it is something that ASUS, MSI, and Gigabyte are all working toward. The only purpose is for reducing cable clutter -- there's no functional (as in, power) advantage to doing this, so the biggest challenge is getting enough consumers to care as there's no real support for cases right now.