Eight rows of Macs, JDW. Certainly, the vertical load is way past the expectations of the original Mac designers. There are a few mitigations, however.
The Mac case design is sufficiently squat that we don't have to consider Euler's column theory. The cases are unlikely to collapse en masse in a cascade (which might happen if Euler was valid). If one case fails, the most likely consequence is that it will exert a lateral load on the Macs surrounding it and onto the walls beyond. Given the constrained space, it is unlikely that a Mac might topple, even from the row above a Mac that has collapsed.
The most dodgy row is #7, where the number of Macs in the row is reduced from eleven to ten, leaving a gap on one side and the opportunity for Macs to fly.
But this is all presumptive. Before stacking up the Macs, what else did the owner do? It looks like a damned posh cellar to me and I find it difficult to believe that "staying up" was not part of the owner's calculations.