Mods like create/ae2 have special placement rules that let you place blocks in specific ways like cogwheels to attach to eachother, axels to stack at length, devices to be placed in correct orientation to energy source by default etc. The (amazing and gamechanging and wonderful) quark varient system, because of how it handles the switching, where the original item is still technically in your hand and not the selected varient, and the selected varient is in a special quark managed slot (from what I understand), leads to any funcitonality like mentioned before with create to not work. That means that, for example if I make big and small cogwheels varients of eachother, one of them will not be correctly placeable as I get the placement rules of the original instead.

The actual request, either:

• Do the opposite of what is done now, meaning the item in your hand will contain the selected varient, and the quark special slot will contain the original item. That will mean making special handling for picking up items because you need to "convert" them while picking them up which is likley more complicated but it would be the best end result solution if possible.
• Document how to support this system with addons so that mods like create will be able to force their placement rules to work according to the varient instead of to the block in hand where applicable