If your primary goal is to expand user base, then yes, supporting the os's that most of the planet uses, is a necessary first step. Once everyone knows what Inkscape is, and uses it, you can use the popularity of Inkscape, (faster updates, for example) to push people to Linux. It's too early to push. It's not easy enough to get Linux onto new machines, and it's not worth most people switching just to use Inkscape, because it is not popular enough. Popularity is a measure of success. It is neither shallow, nor simple.