My current situation:

--I flew about 20 transcon segments (NYC-LAX/SFO/SEA) this year. All but one of them were upgraded, of course only last-minute at the gate after everyone had a chance to buy the seats. (So what is Delta really giving up?)
--Most companies, including mine, don't allow the purchase of business-class tickets on domestic routes, but they don't care what fare of economy I buy.
--I'd often wait until the last minute to buy transcon tickets, which benefited Delta quite a bit because I was paying on average ~$1,000 r/t. With a higher fare class, I was more likely to be upgraded with complementary upgrades or I could use one of the 10 SWUs granted every year.

New situation:
--No more complimentary upgrades NYC - LAX/SFO/SEA.
--New "Regional Upgrade" certificates not usable on this route either (!!!), despite it being domestic.
--Only new "Global Upgrades" usable on this route. Diamonds are to be granted only four per year.

Does Delta really think Diamonds like me are going to want to take 20 transcons per year and only have a shot at getting upgraded on four of them? Does Delta expect me as a busy person to waste time connecting in Salt Lake City or Atlanta on my transcons to have a shot?

These changes are a huge win for bargain-basement Diamonds who don't fly transcons frequently: Current SWUs that require very high fare classes are being replaced by (a small number of) Global Upgrades that are really usable.

For me the outcome is as follows:
--Will evaluate other options including AA (unlimited upgrades on this route for top tier) and UA (gives top tier a total of 12 certs usable on this route)
--When I do fly Delta, I no longer have an incentive to buy a K+ ticket. Will buy tickets where possible earlier and at far lower prices
--Will fly far fewer transcons PERIOD, because for people like me who take 80+ flights per year, spending 5 to 6 hours in coach twice a week is disaster.
--When I fly international, I will be out of Global Upgrades so probably won't fly Delta as much anymore even on my ~$4,000 coach tickets. Previously I had enough SWUs to upgrade these.