Google Discussions Search
I did find out about a useful Chrome extension called Discussions button for Google Search:
It automatically adds this to your search query :
inurl:forum|viewthread|showthread|viewtopic|showtopic|"index.php?topic" | intext:"reading this topic"|"next thread"|"next topic"|"send private message"
It does not pull up discussions from most social media websites or from Yahoo Answers (probably the most common site you would have found in google discussions, before Google axed it.) To get around that, you could install an extension called Popchrom (for keyboard shortcuts) and add one with something like this:
In fact, Popchrom kind of makes the formerly mentioned extension kind of unnecessary, as you could just combine both queries I listed or modify as you wish.
If you have any suggestions for the query examples I listed, they are very welcome.