It is true that in absolute number of users linux audio is relatively small compared to win and osx. But the linux people are in general very tech-savvy, enthusiastic and know of the importance of feedback, especially in open source projects. You say "GPL" and the Linux people will come.
@Christoph-Hart
No, we haven't met. I just googled your name (found your page from ~2013) to see if you are German, because your name sounds like you are. I think it is important to connect and network, especially when it comes to open source audio (linux or not). I am organizing an "Open Source Audio Meeting Cologne" every month http://cologne.linuxaudio.org and it would be fantastic to have you there as a talking guest one day. In our January meeting I will present to them HISE, or rather what I have learned until then.