le jeu en vaut la chandelle

That depends on the journal. When I was in college, one of my professors had stacks of that stuff, and they all had different parameters. Some were about analyzing Tolkien's work, some were linguistic, some were literary analysis, many were a mix, and some were frankly fanfic written by professors. The latter two categories seem most likely to fit your idea. So in addition to looking for journals in the usual fannish places, you could also check university libraries near you -- someone is likely to be archiving whatever the current Tolkien academic journals are, and may also know which faculty are into that stuff so you could also ask them.

I did see some extrapolative articles back then, many of the format "If X, then W." They would start with information from the canon and then discuss what else must have happened in order for that to be true. These appealed to me because I write fanfic "derive in, extrapolate out." So it's a type of writing that has appeared in the field before.