Proposal: Latin Language
Now, I may get a lot of initial skepticism for this, but since most Classicists know both Latin and Ancient Greek, and since the Greek proposal is going nowhere, and since ancient Greek is closer to Latin—not in the genetic sense, but in the cultural sense—why not do a Classical Languages community? Or even a Classics community, for all questions related to the Ancient Mediterranean (perhaps also the Near East?).
This way, people could ask questions not just about Latin, but all Roman literature, even that in Greek, and the literature from which the Romans drew, i.e. Greek, and the contexts of the texts. As of now, history.stackexchange does not do well with questions relating to classical antiquity, and presumably people who have Latin and Ancient Greek questions also are likely to have questions of ancient Greece and Rome (and the reverse is true, that people who know Latin and Greek are the best experts in knowledge of ancient Greece and Rome).
Edit: Just wanted to add one more point that hasn't really been addressed, but Latin + Ancient Greek + cultural and literary questions about ancient Greece, Rome, and their neighbors stands to have a better chance number-wise than being all split up, no? This is similar to history.SE being all history, not just history of one particular nation, region, or even continent.