It's non JEDEC. It's going to be expensive on top of the already-high RAM prices that Samsung is intending to keep high. I can maybe see having the DC DIMMs for professional workstation boards because those buyers may have a justifiable business need, but not for a mainstream Z390 board.
People can't afford even 16GB of ram because of Samsung and others price fixing the DRAM and now openly stating that they will slow down production to "adjust to demand" (aka. keep current fixed prices) and now mobo manufacturers are adding useless slot for some overpriced high capacity ram sticks nobody seen before.
The tall DIMM's remind me of a double decker bus. Might as well call this RAMBUS 2.
"It's too early to tell if the DC DIMM format will catch on."
No, it's extremely safe to say it won't catch on. Workstation users who would want this feature will likely get an 8 DIMM motherboard anyways... Consumer 4x16GB/64GB of RAM is a $600+ proposition, workstation/server grade 32GB DIMM's are $500 EACH, and consumer processors like the 8700K only support 64GB anyways. If you're willing to blow $2,000 on RAM alone, you're not likely going to use a Core series CPU and consumer motherboard either.
The reason people don't have more than 64GB of RAM isn't due to DIMM sizes, it's due to cost and need. I rarely have a use for even 32GB of ram for various editing tasks, and while I accept there are people who have a legitimate NEED for more than 32GB of RAM, most of those users will likely be on a Xeon or X-Series Core CPU with 8+ DIMMS capacity anyways.
This is targeting a fringe group of users who have enough money for a LGA2066 build, but don't want a LGA2066 because... well I can't think of a reason. And I'd imagine the market can't either. I have no idea why they came up with this unless it has a direct server/workstation spinoff with proper ECC support.