Granted, it's intended for servers, but I had not heard of this Deep Mini-ITX Form Factor before. ASRock announced the AMD B550 motherboard B550D4ID-2L2T that is based on exactly that.

ASRock Rack has released the AMD B550 chipset-equipped motherboard "B550D4ID-2L2T" compatible with the Ryzen 5000 series . Deep Mini-ITX, a unique form factor with an expanded width of about 40 mm, is used. A standard ITX board measures 170 x 170 mm, while this Deep Mini-ITX form extends the board towards 170 x 208.28 mm, or 6.7" x 8.2".

The memory slot is equipped with ECC-compatible DDR4-3200 x 4, and up to 32GB x 4 can be mounted. The storage is equipped with M.2 x 1 (22110/2280) with PCI-Express4.0 (x4) connection, M.2 x 1 (2280/2242) with PCI-Express3.0 (x2) connection. The expansion slot is equipped with PCI-Express4.0 (x16) x 1. The network is equipped with 10 Gigabit LAN x 2 by Intel X710-AT2, Gigabit LAN x 2 by Intel I210, and Gigabit LAN x 1 for management.

In addition, the interface is equipped with USB3.2 Gen.1 x 2, HDMI x 1, and D-Sub x 1. The external dimensions are 210 mm wide and 170 mm high.