I'm concerned about the probability of having some technical people get together and solve some incredibly deep research problems before some perhaps-slightly-less-technical people plough ahead and get practical results without the benefit of that research. I'm skeptical that we'll see FAI before UFAI for the same reason I'm skeptical that we'll see a Navier-Stokes existence proof before a macroscale DNS solution, I'm skeptical that we'll prove P!=NP or even find a provably secure encryption scheme before making the world's economy dependent on unproven schemes, etc.

Even some of the important subgoals of FAI, being worked on with far more resources than MIRI has yet, are barely showing on the radar. IIRC someone only recently produced a provably correct C compiler (and in the process exposed a bunch of bugs in the industry standard compilers) - wouldn't we feel foolish if a provably FAI human-readable code turned UF simply because a bug was automatically introduced in the compilation? Or if a cosmic ray or slightly-out-of-tolerance manufacturing defect affected one of the processors? Fault-tolerant MPI is still leading-edge research, because although we've never needed it before, at exascale and above the predicted mean time between hardware-failures-on-some-node goes down to hours.

One of the reasons UFAI could be such an instant danger is the current ubiquitous nature of exploitable bugs on networked computers... yet "how do we write even simple high performance software without exploitable bugs" seems to be both a much more popular research problem than and a prerequisite to "how do we write a FAI", and it's not yet solved.