An even weirder thought experiment.

Spawn eggs can be used on any surface of most solid blocks to create a mob, a type of entity. The only difference here is that boats can be used on water blocks, but I'm pretty sure squids and guardians share this property. Since boats, like mobs, are entities, boat items could be seen as spawn eggs.

I'm pretty sure armour stands could be seen in the same way.

Paintings and item frames do not count since they can only be applied to the sides of blocks, minecarts and their variants can only be placed on rails, and falling blocks must be placed as actual blocks first. etc.