^ It's always possible, but also unfalsifiable. Sort of like "we live in a simulation". There's no way to prove that without proving it (if that makes any sense).
Our Ultimate Corporeal Form, a posthuman starfish
And another thing: humans are tiny. We are much smaller than we think we are. Just look upon the majesty of cumulonimbus clouds shining in the evening sunlight— and know that they are often literally taller than mountains by several times over.
If all space & biomass were perfectly utilized, then every human alive could fit in this cube:
In our current forms, we wouldn't survive being reduced to 100% perfect use of biomass— we'd be about a third of a cubic meter in size and every internal aspect of our bodies would have no space between them— but it does go to show how small you can realistically compress humans.
The average cumulonimbus cloud is much larger than that. Imagine a mountain of water hovering above you, but that mountain is twice the size of Mount Everest.
Every human alive could probably fit into a single storm cloud, even without being compressed.
Now consider the possibility of posthuman-tier technology allowing us to escape the confines of a primate form. Theoretically, a posthuman could become much larger than any storm cloud. Perhaps even the size of a planet. The computing resources alone would be fairly extreme, but managing such a large size would certainly require a greater intelligence & capacity for homeostasis than we humans currently have. It might be better to imagine it as a quasi-ethereal borg of posthumans.