Of course. That is always the case when doing cross platform work. You code to the lowest common denominator. This is a concept that is already familiar to web designers having to code for several different browsers. You either keep it basic and compatable, use the clever features of one platform and exclude access from the rest or you can re-write the clever bits once for each platform using the proprietry technique available on each.
I didn't say it would hard, just not a priority for *nix users. And C# being more professional thing is just a hangover piece of snobbery from the C/C++ vs. VB6 argument. In .Net there is no real difference between the two and certainly no speed advantage to use C#. The main difference comes down to which syntax you prefer.
You're not kidding! :) Of course, you're assuming that that is their original roadmap and not one that keeps getting revised as deadline come and go!