How about looking at this mathematically?
Soarin's capacity is around 1300 guests per hour with a capacity of perhaps 15,600 guests per typical 12-hour day at Epcot. Assuming about 60% of Soarin's capacity is allocated to FP+, there should be about 9,360 Soarin' FP+ per day. With Epcot's average attendance around 30,000, people have less than a one-in-three chance at a Soarin' FP+, even less during popular periods such as Spring Break, Summer, and holidays. Furthermore, that's throughout the day. If Disney offers a Soarin' FP+, it could end up being for 9:00 AM or 8:30 PM. The chances of people getting Soarin' FP+ at the times they actually want are are slim indeed.
If Disney holds back some Soarin' FP+ for "day of" guests, then even fewer people will be able to book a Soarin' FP+ prior to arrival.
Yes, it will be difficult to get FP+ for WDW's most popular attractions.