IMHO, TSM, ToT, RnRC, and ST are DHS's marque attractions and the only attractions at DHS that should have FP. (Unless you feel no attractions should have FP.
) Depending on what numbers you trust, combined capacity is around 6,500 guests per hour. (Reported capacities for some of these attractions vary wildly.) Assuming a 12-hour operating day, this equates to a daily capacity of 78,000. Not all capacity is allocated to FP. Reports vary so I'll assume a middle ground of 55%. This means there are about 43,000 FP available for these 4 attractions.
DHS averages 26,600 guests per day. On busier days, attendance will be much higher. Even with longer park hours, guests should be able to average 1-to-2 "good" FP+ for DHS's 4 most popular attractions. Disney will have to create a lot of "filler" FP+ (think LMA) in order to meet the "3 FP+ per person" requirement.
Let's also recognize that the Standby line for TSM can be longer than the
combined Standby lines for ToT, RnRC, and ST. TSM FP+ are really "valuable".
Since I know how to game the current FP system, I know how to get a lot more than 3 FP per day at DHS. I'm sure most experienced WDW guests can do the same. Experienced WDW guests will lose as a result of FP+. Inexperienced WDW guests will gain.
Since MK has so many "good" attractions, I suspect guests will be happier with their 3 FP+ choices at MK.