Not as big as Linux but I know a few FreeBSD shops that run NodeJS apps so it's not entirely crazy to think that there are more and they would want to try Deno. Besides making your OSS software compilable on *BSD/Linux/Mac/Win has historically been a good thing to do anyways.
For a lowlevel runtime (ie V8 itself) I can accept certain lag since there might be some low-level differences in how signals,etc behave.
However for more generic code Linux'isms often signals a certain "works-on-my-machine" mentality that might even hinder cross-distro compatibility, let alone getting things to work on Windows and/or osX development machines.
I guess a Rust binding for V8 is a tad borderline, not necessarily low-level but still an indicator that there's a lack of care for getting things to work on other machines.