Sorry let me clarify what I meant. The five elements have individual elemental planes, but the element of spirit is often expressed as animus or sentience, so it a plane made from spirit would likely have sentience or strongly support it. I merely expressed the thought that the abyss was a natural plane of spirit as sentient beings are very hard to kill in the abyss and recover at improved rates. It is also easy to bring animus or spirits into the abyss and very difficult to bring other elements into it. I don’t know what the other elemental planes look like so this is all conjecture. The abyss is weird and spirit is the only element that I can think of that might actively try to bring others to itself through pure willpower. For all intents in purposes a plane of spirit could simply be a collection of sentient thoughts originally. Most sentient beings prefer to have a body to protect their spirit, hence they might over time create a new plane for themselves. This intelligence could then craft the realm so that they might interact with those planes around them. Spirit is weird and I have know idea how it would look, but each plane of spirit could act differently as they might possess sentience and would make them harder to recognize than other elemental planes that would act on set rules.