The D-11 is the first to reach the 32 skin limit. Looking on the skins page there are some other aircraft in danger of reaching it as well. As this page hasn't been updated in ages it is impossible to tell how few slots are really left but the following all show less than a dozen available: the 109E, F, G-2 and G-6, the B-24J, the P-38J, the P-51B and D, the Spit 5 and 9.
I'd say most of the D-11 skins are actually later variants.
