To those on a budget shopping for 2014 minis: Although the 1TB Fusion Driver (1.1TB, really) is indeed a paid upgrade, it feels really fast, dare I say as fast an older mini with a fast "pure SSD". The OS X implementation of Fusion Drive seems so solid, that I never notice there is a traditional hard drive in there supplementing the PCIe SSD. Normal tasks on the late 2014 mini seem just as fast as my Late 2013 Mac Pro with PCIe SSD.
Yet some still speculate that the Fusion Drive is a somewhat crippled "transitional" form of storage technology.