Spoiler!
The difference is obviously not huge, but all surfaces pick up lighting just a little better with linear colour space. Note the tapestry on right-hand side and how pattern is darker and more distinct in second screenshot. Even without mods, the textures feel a little bit richer.
There are some issues that would need to be resolved. The tilemap shader for exterior terrain needs a fix to sample tiles correctly, fog and lighting will need re-tuning to look their best, and mods will almost certainly need to be recompiled. But the game otherwise runs fine with linear colour space and looks better for it.
If you run DFU in the Unity editor and would like to play with this yourself, enable linear from Edit > Project Settings > Player then setting "Color Space" to "Linear" under "Other Settings". Just ignore the terrain tiles for now, as I mentioned above this shader requires a fix to work correctly with linear.
I'm interested in feedback from other devs on the forums, whether you've worked on DFU or not. Linear colour is generally recommended for better lighting workflow. If DFU didn't begin in the Unity 4.x days, it's quite likely we would have started with linear from the outset.
