Schneider has had an 82mm 10-stop ND for a while (in fact, when I bought it in 2011 they were the only game in town for an 82mm ND3.0 screw-in).
Ok, in this case I was unable to find it for sale anywhere or simply forgot about it after seeing the price :-o
But concerning the original topic: I just stumbled across a link about "IR Pollution" that doesn't just result in a color cast but lower contrast, and this is said to be fixable with a combined ir/uv stop filter: http://www.leeduguid.com.au/blog/tips/bw-10-stop-nd-filter-nd-110/
However, this filter has a big drawback: "Interference filters do not work well with wide angle lenses; light rays entering at an angle cause differing color rendition, resulting in increasingly cyan corners. It should not be used on lenses with an angle of view wider than 60° (about 35mm on a full-frame 36 X 24mm sensor)."