Hello.
First of all, I am in no way related to the FSB plugin, so this is just my private opinion:
0. Apparently, developers do not answer these threads.
1. It is relatively easy to add a “Share on Diaspora” to the list of existing social networks. Due to the existence of third-party services (like this), all it takes to ‘glue’ them is a couple of lines in PHP.
2. From a developer’s perspective, the real question is whether the result is worth the effort. Diaspora is still very small, so, comparing to the other buttons, a “Share to Diaspora” button will generate very few clicks. Moreover, I suspect that most users will no even bother enabling it.
Best regards,
Vitalie Ciubotaru
P.S.: I am the developer of the “Share to Diaspora” plugin that you mentioned in your message.