it also puts me in mind of perhaps the first (pre-Tolkien - it predates LotR by several decades) modern high fantasy novel, ER Eddison's The Worm Ouroboros, which is written in meticulously reconstructed 17th-century style prose.

Ahem. Excuse me, Wood Beyond the World by William Morris predates The Worm Ouroboros by a few decades. It directly inspired Narnia, and indirectly inspired LOTR. And it is written entirely in reconstructed Chaucerian English.