The 1680 v2 had 25MB of cache (the addition 5MB of the two cores flipped off) . The 1680v3 has only 20MB. So yeah it is in the same die as the rest of the 1600 line up.
http://www.anandtech.com/show/8423/intel-xeon-e5-version-3-up-to-18-haswell-ep-cores-/4
Some of the backslide on turbo is probably in part coupled to not enough data to keep it fed. Keeping it cool in a tighter space is another. But the 1680v3 is actually listed openly in ark.intel.com. Have to use google search to get to the 1680 v2 page. For whatever reason though Intel has stuck with the quirky price (puts loads more money in their pocket no doubt). It should be a bit lower than that (-$200 or so). We'll see when v4 arrives. Probably depends upon how hard Intel pushes the base/turbo rates up.
4-6 options isn't really alot (could be split into two major sub groupings). They have also lost a small amount of creditability with the "millions of permutations" that is suppose to be a 'insanely great thing' for the Watch in contrast with the you can only choose from a list of 3-4 dogma.
Apple surrendered to the Internet ( not using Appletalk all that much anymore.) In Steve Jobs Flash rant didn't he say that Apple likes standards when appropriate.
M2 is a bit "too loose". There are multiple form factors and 2-3 years ago there was really no solid consensus from PC industry that they were going to adopt. The new Samsung 950 Pro M.2 is going to be sold at retail. The previous Samsung high end PCIe SSDs were not ( OEM only). The question of whether the slim stick format closest to what Apple implemented was going to be adopted broadly or not is apparently over. It is being sold at retail by major suppliers.
It is probably cheaper for Apple to buy. They buy standard connectors and standard parts. Slap their own firmware on them. Same reason why buying Intel and buying ARM architecture license is cheaper. Share R&D costs with others and get better, more affordable products.
Apple had a bug up their but over TRIM. But if over that..... cost, support, and ease of buying wise ... it is better if buying from the industry. If Apple got to point where they rolled their own high end controller and were just buying flash chips in bulk ( like the iOS devices ) to solder onto the board then standards wouldn't make much of a difference. For now though, removable storage is good. High amounts of write activiy means the SSD is likely to wear out before the Mac system will.
It is better that Thunderbolt is somewhat widely adopted than Apple Display connector that went no where fast.
Apple already set the trend before the standard was really dry. Almost all the Macs are stick SSD only.
this is one of those things like EFI where Apple is more so waiting for the PC industry to catch up to the trend that is already moving.
Bend? It was fundamentally the same thing electrically. Primarily the physical key notches in the connectors were different. The dimensions of the board were slightly different. More different for difference sake than a "bend" in direction long term.
Not at this stage. The design has been frozen. And in retrospect not too surprising that Intel traded PCIe 4 for their own in house interconnect after spending many many millions to buy it. Intel bought Aries / True Scale. Omni Path is a follow on to those (
http://www.anandtech.com/show/9561/exploring-intels-omnipath-network-fabric ).
Lots of boards haven't fully taken advantage of PCIe v3. Cranking the speed of PCIe v4 even higher is likely going to be at least as bumpy as the transition from v2 to v3 was. Sandy Bridge was late because of that. The folks highly demanding PCIe v4 were mainly the Infiniband and 100GbE folks. Intel's Omni-Path is better near term route that probably will be more cost effective. AMD barely got to PCIe v3 and who else is in hot persuit. ( Power and Sparc are also messing with other stuff also. )
Just doing 8 more PCIe v3 lanes is easier. Some folks can plug in more x16 and x8 cards and board vendors can solder on more 10GbE , Thunderbolt v3 and sockets for M2 x4 PCIe v3 SSDs.