I would not really know how to do this even if it is possible, but I was wondering, is it possible, using NifSkope, to add nodes on the human skeleton on which more items could be equipped? Even if it could be done, I expect it would cause major mod incompatibilities, but I don't really know., but i think it would be prety cool. Does anyone know?

I don't believe you'd have any problems adding lots of extra skeleton nodes, but what you won't be able to do is have them recognized as attachment points for anything. There's no known way of defining an extra slot for mesh replacement.

Take rings for example. There are mods that allow unlimited rings, but the engine allows only two to show, and nobody has been able to change that, even though the digits of the hand are all already present in the skeleton. Just having a location isn't enough.

It is impossible to add more equipment slots, it is hardcoded in the game. The slots dont even need to be relevant ot what you are putting in it....i could put gloves in the legs slot....however that would cause the legs to disappear. The mesh/skeleton only controls what items are rigged to, it is in no way connected to equipment slots.