I'm going to answer my own question.
I have found the NodeBB Featured Threads plugin.
With this one I can stack the posts I like to show.
Jan 1, 2014 - 420 posts - ‎33 authors
for example. It doesn't show the number of authors and posts in each topic for SEO purposes. This should be pretty simple to add.
Two things:
display: none;
or behind a javascript tooltip (since that won't get called at all). If you show it for non-js, and hide it with js, chances are Google might detect and penalise, so even worse