I really want to comment about it aesthetics... But really can't since all one would see if a gpu and heat sink. That is neat, and can see the practical application for developers on the move.

Bruno747
I have been impressed with the way they manage to cram so much stuff into a thin small chassis.

+1, I'd put myself in the category that I'd get it if I could afford it as it fits the bill of exactly what I want.  I don't see the point of sacrificing performance for making it smaller, so I probably would pay extra to get it done.  If the CPU and SODIMMS were soldered on, then I could see the board get smaller than minITX as the socket and slots aren't needed, it could end up as a picoITX (except the board is too small for PCIe x16 slots).  

TPUAvailability of aftermarket DDR4 SO-DIMM memory is close to non-existent, but that could change with 6th Generation Core processor notebooks hitting the shelves by Holiday 2015.

I think this was the hitch before, although the current model with dual regular DDR4 DIMMs is retail less than $300 MSRP, newegg has it for $250.  I'm sure this newer version will soar above that, and it doesn't even overclock.  

If there was a way to add on more PCIe slots without taking space on the board (i.e. PCIe external cable), that would make it even more expensive.

Limited for SODIMM Memory and Cost is High. They are also hard to find.
8GB DDR4 PC4-17000 Unbuffered ECC 1.2V 1024Meg x 72 $138.99
16GB kit (8GBx2) DDR4 PC4-17000 Unbuffered ECC 1.2V $277.99
32GB kit (8GBx4) DDR4 PC4-17000 Unbuffered ECC 1.2V $555.99
http://www.crucial.com/usa/en/memory/DDR4

Just look up the board on AsRock's site, no support for regular Windows 7/8/8.1, only server versions and other OS'.  With no i7 support and using a C612 chipset instead of X99, it is clearly not for enthusiasts.