LOTR RPF qualifies, as we only have about 3,200 works on AO3. Right now, the nomination list only has Sean Astin and Elijah (scroll to RPF and open the section).
The process is pretty much like Yuletide. In the FAQ, they suggest that only people planning to participate in the exchange submit nominations:
You may request up to 4 fandoms, minimum of 3. The maximum of characters you can request in one fandom is 4. If you’d like to request fic about a group of characters, don’t forget to nominate the ensemble during nominations (as an example, on AO3, The Lord of the Rings fandom has a character tag called The Fellowship of the Ring to denote a specific group of characters)Here are the Nominations Page and instructions -- nominations closing April 12 at midnight Pacific time
Hope someone will enjoy this, thanks to lbilover for explaining this. A shame it's for fic and not other kinds of fanworks too.