The HP Z6 Workstation ($1,919) dials that craziness down a notch, with 384GB of max system memory and fewer slots and ports, but still has the dual Xeon CPU option. The Z4 Workstation ($1,239), meanwhile, lets you install 256GB of RAM and a single Xeon CPU, limited to Intel's new W-series. The top end of that right now is the Xeon W2155 with 10 cores and 20 threads, and HP hasn't said whether it'll support the flagship 18-core Xeon W that's coming later in the year.
Remember, these prices are for the bare boxes only, not the graphics cards, memory, CPUs and other stuff you'll need. On the Z4 model, however, the Xeon W 10-core chip is "just" $1,000, so it should be no problem to build a box for around $3,000 to $4,000.
HP also unveiled a few new displays, including the 38-inch Z38c curved display that is a bit of an odd duck for HP's video-oriented Z lineup. Much like LG's 38UC99 38-inch screen, it has sort-of 4K resolution (3,840 x 1,600) 21:9 that can't actually handle full-resolution UHD video, so seems more suited for gaming. It also lacks other features like 10-bit capability, which is becoming increasingly important for 4K HDR video editing and color correctoin.
HP's Z8 and Z6 Workstations are coming in October, while the Z4 arrives sometime in November. This end-of-year date should help film and VFX houses fit them into their fiscal purchase budgets, because other than the Z4, these aren't really meant for you or me.