How exactly you will enjoy it, I'm curious? Any kind of highly professional work, I figure. But any professional should've (and could've unless one's actually not) invested in X79 with its 51.2 GB/s quad-channel base theoretical and 64 GB total. Well then, congratulations, anyone has been able to sport 32 GB for near two years in... well, ok, four slots, albeit running much faster than two and, I bet, for the same cost.
Density is primarily what I'm excited about, but more clock and having more memory on the same silicon can only boost performance. I don't know of any 4-slot mini-ITX. You can get full performance including full size video in a Mini-ITX with ease now, but not 4 mem slots. When it gets to servers, of course, the more memory you can get in a single VM Host, the more money you save on licensing. With VMs memory equates directly to VM performance here. 64GB is nothing in the enterprise. We're looking at Terabytes and many slots. The fewer the better.
I would imagine the performance boost from the clock specs on DDR4 will be much higher than moving from dual to quad channel but I have no experience with quad channel. With an 80% performance boost, and based purely on clock and density, I believe it can come close, this will provide significant performance for OS and applications.
DDR4 will mean we we might actually experience DDR3's theoretical top end if the numbers translate to real world performance. It's a natural and expected evolution. Once devs can assume high end gamers realistically may have 32-64GB, 32 even in a Mini-ITX, they will utilize it and with 64 bit game engines like Frostbite, I'm excited to see how. It's still a ways off, or from being mainstream affordable after that, but it's definitely a good thing.