Most people are missing the point. LLMs are not the be all end all of AI. Even if you were to say memory bandwidth was the problem, there is no consumer grade GPU that can run any SoTA LLM, no matter what you'd have to settle for a more mediocre model. Outside of LLMs, 256 GB/s is not as much of an issue and many people have dealt with less bandwidth for real world use cases.
What other use cases would use 128GB VRAM but not require higher throughput to run at acceptable speeds?
The only likely difference with DGX Spark is that it'll be a more desktop-centered platform, what people can do with it, not sure, but say for VR, the DGX Spark is basically the best compute puck for one right now.