There is the 'share' module you could require. The problem though is, that it doesn't expose the needed function addHandler. openShare as well. Is this by design?
Otherwise I might just look further into it and introduce a hook, extend the ACP or something, not sure yet. Suficed to say, that this generally is on my list for a week now, since plugin-smoothshorts would make use of something like this, as well.
@rbeer Thanks. Sorry to be a critical asshole at this point but then stop calling nodeBB "community" software when it's a major adventure to add social sharing options. Every forum software lives in the past....we are in 2015 now......The world is all about social media!
@Blue-Orange
Point well taken. 
But please bear in mind, I myself am fairly new to the software and its code. I should've pointed out, that I might be wrong about what I wrote there.
As for the word "community": I think the slogan tries to transport the idea of enabling you to create a community. Obviously, interconnected services are the way to go, nowadays. But from what I've seen so far, the core team (which I'm not a part of) is mostly concerned with making the internal community's (as in: your community in your forums) experience as enjoyable as possible. And finally: The sharing option is quite new, that's true. If I'm not mistaken, your request here is the first of its kind (i.e. sharing to other services than the big 3). It's a little bit like with every new road, where the tar is still boiling hot: It's bound to throw some bubbles. I'll wait a few days for any vetos to arise, because we are talking about core changes here. There;s nothing worse than breaking the core - then It'd be mayhem all around. Also a reason why changes sometimes take a while. I think it's in everyones interest to take some time and get it right, rather than doing it in a hurry and plowing everything over along the way. 
If that hasn't happened then, I'll jumpstart my steamroller and see what I can do. 
As stated, it's in my interest, too.
What, btw., do you mean by "buffer button"? This little menu attached to every post, right? 
Oh... See! I would've done complete nonsense if I hadn't asked. 
Well, this then is actually a completely different story, indeed. This requires adding an UI element, rather than changing present ones. In fact, it would be reasonable to leave it out of the core overall, as it's matter of taste whether you would want to use it or not.
Are you familiar with the template engine used (templates.js)? I'm not much of a UI guy and if you used it before, I would guess you are familiar with buffer-buttons and how to embed them (HTML/CSS). Maybe you could place those buttons in the (your) theme and I'll provide the needed data from the backend (i.e. plugin).
I really gotta sleep. 
Needed like 10 minutes for those few lines now. xD
But I'm pretty confident, that this is not too complicated, after all!
