I'm surprised this hasn't been asked before, I did a brief search through and couldn't find anything.
There are WIPs which are high quality enough that I listen to them along with my other favorites posted on the site. Problem is these WIPs were last updated a year+ ago, so the remixer probably stopped working on it. If they were to see a few posts from people reminding them they had something really good going, the morale boost might inspire them to finish it.
So, options on how to do this:
PM the remixer. But this means that only one voice is heard, and that voice might not be one well known in the community like yours truly, so it wouldn't be too significant.
Thread necromancy. Is this frowned upon (if the thread is still even available)?
Start a thread specifically dedicated to people listing WIPs of high quality which they'd like to see finished. Thing is, eventually this would turn into a monstrosity of a thread that's really no longer of any value. Maybe there could be an annual thread of this nature, the "votes" are tallied, and the 3 most popular WIPs are listed (at which point that year's thread is locked). This might be enough to inspire the remixers anyway, but maybe also if one of those remixes is completed and accepted to the site, the remixer gets a prize of some sort like one of your cool hats. Obviously not my call there.
Thoughts?