Sign me up! I would love it if they did this in Middle English, but I’m highly doubtful they will.
If Robert Eggers aims for “dialogue true to the time period,” it doesn’t necessarily mean full Middle English, which would be largely incomprehensible to modern audiences and would require subtitles—something that seems less likely for a mainstream horror film. Instead, he might use a stylized form of Early Modern English.
Mel Gibson was able to make Apocalypto entirely in Yucatec Maya largely because he financed the film himself through his company, Icon Productions. This gave him full creative control, allowing him to take risks that most studios would never approve of.