During its WWDC 2019 keynotes, Apple also announced the upcoming Mac Pro Expansion (MPX) model, which will feature passive cooling that allows the stacking of multiple GPUs. They'll utilize Infinity Fabric Link, which is 5x faster than PCI bus, and there can be up to 2 MPX per each Mac Pro. This could be offered in addition to a standard third-party GPU, which is a boon for those looking to purchase a Mac Pro in the future.
The fanless design with a massive heatsink can include up to an AMD Radeon Vega II GPU with 32GB HBM2, and combining the two gets you up to 28 Tflops of performance.
The new Mac Pro itself starts at $5,999 and will ship this fall. Apple made sure to note that a PC with similar specs, however, would cost over $8,000.