It's about time. I was bullish on the Fusion Drive when I first got my iMac 5K. In theory it's the best of both worlds and the performance is massively better than an HDD and a lot cheaper than an SSD of the same size.
What they don't tell you, though, is that the SSD part of the Fusion Drive gets absolutely hammered with wear as you use it.
Data is constantly being migrated onto and off of it as you work. (That's by design -- after all, the logic is that the stuff you're actively working on is moved to the SSD). But all that throughput, with the tiny SSDs Apple provides in these systems, destroys them with wear. After about 4 years, the 128GB SSD in my Fusion Drive was showing less than 10% of its lifetime left before I opened the thing up and installed a big SATA SSD. So, as far as I'm concerned, Fusion Drives are basically a ticking time bomb. Also remember, some of the SSDs in Fusion Drives are a measly 32GB, exposing them to even worse wear rates than mine.