Funnily the current high end Mac Studio are not suited for current LLMs. M3 Ultra is "quite an old" chip for AI, despite its bandwidth. The issue for running local models (especially LLMs), you need few things to align really well: 1) compute power (affecting PP) 2) VRAM capacity (affecting model size you can load) 3) Bandwidth (somewhat affecting decoding speed).
The issue with the M3 chip is the compute performance, as it doesn't fit well the transformer architecture. This changed with the M5 (apple baked their own matmul into the chip), which would significantly speed up PP (and video/image generation btw), making the M5 Ultra significantly faster than the M3 Ultra and in practice much more usable. You can try to load Kimi or GLM on M3 Ultra, but it's not usable. Now the M5 Ultra is not out yet, but undoubtedly it will be a superior offering, and shilling 15k on 512GB version is actually reasonable (if it's every priced remotely around that tag).
By the way, they cut the supply because they run out of RAM. They still sell the 96 GB model. Everything else is gone, no stock, they cannot manufacture them. Even minis are 48GB max!