Friendica federates well and uses well defined zot protocol so any one wanting to write extension to other services can easily do that. It federates with statusnet and even with propreitary platforms and it can do a lot of more cool stuffs including authenticated zrl's (Zot url's) which will allow only authenticated user to access posts. On the other hand what does Diaspora do other than having nice UX?
People have already invested in Diaspora once but it didn't do very well why do you think people need to invest again? May be providing some strong points other than simply saying "online privacy" will help people to see if its really worth contributing again.