Only having an oral form does not mean people only thought through speaking: one can draw in the sand or link ideas to physical objects.
Nowadays, I’m pretty sure most people are able to develop and think about ideas while constructing diagrams or 3D objects in their head, before writing anything at all.
Now, perhaps a revolution of writing might not be the next step: a helmet imprinting an idea or an image in your mind instantly would change a lot of things.