I have read a suggestion that MAISON.DIEV was originally a misreading of MAISON.DIAV. - itself short for Maison du Diable, recalling Italian titles of the 16th century, such as "Casa di Diavolo" and "Pluton". There is also a "Casa del danato" (House of the Damned) and a "Casa di Dio".
Of course, it is called "Thunderbolt" and "Arrow" and "Fire" too, so it is a very varied card.
However, a simple "misreading" seems to be an improbably reductionistic explanation.
But having read JCs remarks on the title, I think he is correct to note that the form is always "Maison Dieu" never "Maison DE Dieu". The French title is "God-House"; where God lives, I am sure. So perhaps a part of it is Mount Sinai, where the Law, both written and oral was given, and Moses saw the burning bush that was not consumed. In the earliest exemplar of all, that of de Gaignières (Charles VI), the Tower looks much more mountainous than in succeeding versions, and one can imagine the cloud-covered, thunderous mountain of God. Or the Gods, Olympus. I have also considered the card as Hell, or if the Devil be given that job, then Purgatory. Purgatory is portrayed like such a mountain in medieval depictions, and Dante manuscripts; I cannot recall if it is a tower. It leads through fear and punishment out to Hope, the Star, and then upward through the planets to Paradise.
Certainly the most varied names of any card, historically speaking.
Ross