If we're talking about the temperature of things in space- Kelvin would be the norm as absolute zero is the most relevant reference point. It's not like you're getting out of that spacesuit to sunbathe while you're planetside.
Not only that, but it's probably reasonable to assume that our pilots are pretty well-versed in scientific notations and their associated units considering how exploration is basically just applied astrophysics. When you are exploring unknown worlds, working in Kelvin would massively simplify any kind of calculations with regards to atmospheric pressure or anything thermodynamics related. Plus, in all probability, the Fahrenheit scale will have died out in a few centuries time - as the old joke goes "There are two types of American, those that went to the moon and those that use Imperial".
If all else fails, just consider it to be educational! While ordinary average Joes might not use Kelvin today, the moment you step into any kind of science or engineering they become the norm and usually the first step in any calculation is to convert the units to Kelvin. It's actually pretty easy to eyeball things once you get used to it, particularly for lower temperatures, while for higher temperatures it's effectively within error margins compared to Celsius (+273 doesn't make much difference once you get into the 1000s of degrees).
And trust me, if FD actually implemented Imperial units across the board you would start to get very confused. Even people that swear by Imperial units barely know how to use most of them. Most people would rather see 4.37400 km on a readout rather than "2 miles, 5 furlongs, 7 chains, 1 rod, 3 yards, 2 feet and 11 inches"; and then some goon'll ask whether the miles are terrestrial or nautical.
o7 Fdevs and cmdrs!
