"[Noun] upon [noun]" — singular or plural?

I am copy-editing a manuscript in which the author has written the following sentence:

Rank upon rank of theologians has envisioned God the Father as the omniscient and omnipotent one.

"Rank upon rank" suggests plurality, so my instinct is to change "has" to "have". Am I right?

Alternatively, I'm tempted to suggest a more invasive change to avoid the awkwardness altogether. I suspect, however, that I personally do not understand how to handle countable and uncountable nouns with verbs, and I don't want to push this author unfairly toward a less creative sentence in the meantime.

In "Rank upon rank of theologians" the subject is "theologians", not "rank", and the whole noun phrase acts like a plural, so the verb should be "have".

Examples from the Corpus of Contemporary American English (COCA):

• Amid the destruction in places like Bolivar Peninsula and Galveston, where row upon row of houses were scoured from the landscape ... — Associated Press, 2008.

• On this particular day, their services were desperately needed in Maine, where mile upon mile of wild blueberries were in bloom, just waiting to be pollinated. — SPOKEN, 2008.

• RANK UPON RANK OF 400-FOOT SANDSTONE TOWERS DOMINATE THE CENTRAL THIRD OF SAND TANK CANYON... — Backpacker, 2007.

• Layer upon layer of limestone lie so close to the surface that the grasses absorb calcium... — Southern Living, 2003.

  Note how limestone isn't even plural here.

• The small cemetery takes on a magical, cathedral-like beauty as row upon row of candles are lit, opposite. — Americas, 1995.

Likewise for after:

• Thousands of zebras upholster the valley below. Wave after wave of them kick up pink dust in the last flush of daylight. — Smithsonian, 2011.

• Wave after wave of young people come to my house and I keep telling them... — New York Times, 1999.

• ... tiny McClellanville was almost obliterated, and mile after mile of foot-thick pine trees were snapped off like so many toothpicks in the Francis Marion National Forest...  — Saturday Evening Post, 1990.

Rank upon rank is considering only one rank at a time. Compare with every rank which might also connote plurality, but which takes a singular verb for the same reason: each rank is identical.

I agree with @Andrew Leach's observation; by using the word "rank" you are setting the consideration of the sentence to one rank at a time, so the verb form should be singular despite its adjacency to the plural "theologians".

Others will disagree, and say that the verb should agree with "theologians", or that "X upon X" is implicitly plural. Either way, some significant portion of the reading population may find the sentence a bit jarring.

To make the agreement easier, you could change to

Ranks upon ranks of theologians have envisioned ...