Apple added three new MPX modules with latest AMD Radeon Pro GPUs.

AMD Radeon Pro W6800X

60 compute units, 3,840 stream processors

32GB of GDDR6 memory with 512GB/s memory bandwidth

Up to 16.0 teraflops single precision or 32.0 teraflops half precision

Infinity Fabric Link connection enables two W6800X GPUs to connect at up to 84GB/s in each direction

Four Thunderbolt 3 ports and one HDMI 2.0 port on card

Two DisplayPort connections routed to system to support internal Thunderbolt 3 ports

Support for up to six 4K displays, three 5K displays or three Pro Display XDRs

Full-height MPX Module fills an MPX bay and uses extra power and PCIe bandwidth

AMD Radeon Pro W6900X

80 compute units, 5,120 stream processors

32GB of GDDR6 memory with 512GB/s memory bandwidth

Up to 22.2 teraflops single precision or 44.4 teraflops half precision

Infinity Fabric Link connection enables two W6900X GPUs to connect at up to 84GB/s in each direction

Four Thunderbolt 3 ports and one HDMI 2.0 port on card

Two DisplayPort connections routed to system to support internal Thunderbolt 3 ports

Support for up to six 4K displays, three 5K displays or three Pro Display XDRs

Full-height MPX Module fills an MPX bay and uses extra power and PCIe bandwidth

AMD Radeon Pro W6800X Duo

Two W6800X GPUs, each with 60 compute units and 3,840 stream processors

64GB of GDDR6 memory (32GB per GPU), each with 512GB/s memory bandwidth

Up to 30.2 teraflops single precision or 60.4 teraflops half precision

Onboard Infinity Fabric Link connection connects two W6800X GPUs at up to 84GB/s in each direction; external Infinity Fabric Link connection enables two W6800X Duo modules to connect four W6800X GPUs

Four Thunderbolt 3 ports and one HDMI 2.0 port on card

Four DisplayPort connections routed to system to support internal Thunderbolt 3 ports

Support for up to eight 4K displays, four 5K displays or six Pro Display XDRs

Full-height MPX Module fills an MPX bay and uses extra power and PCIe bandwidth

WCCF TECH provides an excellent review of the W6800X, W6900X and W6800X Duo MPX modules.

W6800X is an excellent GPU

W6900X is significantly more powerful than the W6800X

Despite potential losses from the onboard Infinity Fabric connecting the two W6800X GPUs in the W6800X Duo, the performance jump from the W6900X is more than significant.

I would like to see a W6900X Duo; however, there are questions surrounding two 300 W W6900X GPUs exceeding the power ratings of the MPX modules which cap out at 500 W.

The power issue seems to be answered by checking the TDP of the W6800X Duo against the W6800X:
W6800X: 300 W
W6800X Duo: 400 W

Double the GPUs, add 100 W - good new for a W6900X Duo

A W6900X Duo could stretch its legs to 450 W if needed; the power

Oddly, AMD announced the non-MPX W6800X but not the W6900X.