Yes, that's fine. The following would perhaps be a slightly nicer:
static var nan: Float8 { Float8(bitPattern: 0b0_1111_110) }
static var signalingNaN: Float8 { Float8(bitPattern: 0b0_1111_010) }
We don't currently do this for standard library floating-point types for weird historical reasons that are surprisingly uninteresting, but it's an infinitesimally better choice looking into the future.¹
¹ So infinitesimal that I hesitate to bring it up, because it's due to oddball runtime shenanigans that are extremely unlikely to ever be used and therefore really not worth wasting everyone's attention on. There's like a .001% chance of it ever mattering, so basically forget we had this talk.