I'd say don't worry about it. No formal testing needed for non-Windows platforms, at least for level code. The game is targeted towards Windows. If someone notices small problem affecting platform compatibility, and it's easy enough to fix, by all means make the effort. That's about as far as it should go. Plus, it's unlikely level code will be platform specific. You'd have to be doing something pretty custom, and likely bringing in outside APIs.
For game mods I'd appreciate a little bit of concern over platform compatibility, particularly since things currently are portable, though I don't think it needs to be a blocking issue. I like that the NetHelper works on Wine now, but it would still be useful even if it didn't. We should probably make an attempt to test on other platforms as a final step before a new release, though this doesn't need to be addressed while still working on a release. Primarily testing should be done on Windows. Actually, testing on other platforms after a release should be fine. Any problems are not likely to be urgent, and can be patched up after the fact.
Testing after the fact pushes work on the few oddballs who insist on running something different. That's fine. We have limited development resources, so we should try to keep the development burden low.
