Well, there are other reasons not to stack so many filters. First, with a full frame camera, you will likely run into detrimental vignetting fairly quickly...it wouldn't take more than a couple of standard (non-slim, which are not stackable) filters to cause several-stop vignetting.

Vignetting aside, filters, even the best of the best, tend to be of lower optical quality than the glass in the lens itself. Even a single filter, including those of high quality, WILL have an impact on IQ. It is usually low enough that it doesn't undermine the value of using the filter in the first place. Filters also tend to have less capable coatings on them to prevent flare and ghosting. Modern lenses (not sure about the EF 16-35mm I) often have nanocoatings, which are vastly superior to multicoatings. Midrange and lower end filters often have only a single coating, and cheap ones at that. Flare can become a significant problem when stacking filters.

The issues aside, assuming you do not run into flare, the vignetting caused by deeply stacked filters can actually be used to an artistic end. I've found a number of ultra long exposures on 500px and 1x that had extremely deep vignette that I actually found quite pleasing. Any tool can be used to good effect, so long as you know what to expect and put the outcome to good use. ;)