First, certainly sounds like an interesting world build, with several elements that a lot of people would find compelling. Give it a good name, and find or create some art, and I would think you could find an audience for this should you want to expand beyond solo play.
As for the spear only world, there are a lot of neolithic weapons which fill the niche of the sword – war hammers, hand axes, ‘proto swords’ edged with obsidian or shark’s teeth, daggers, throwing sticks, shortened spears, and various other weapons.
We cover a lot of these in our weapon book and some of them are in the core rules.
For a deeper dive into this stuff, I’d recommend Sir Richard Burton’s “Book of the Sword”. It’s a little bit fantastical but he gets into the pre-historical origins of swords, ‘proto-swords’ and many other related weapons.
One interesting theory he had, which I learned subsequently may have some legs, was that swords seem to have “evolved” from a range of ‘throwing sticks’ and ‘throwing woods’, some of which end up with a use and a shape similar to hunting boomerangs. There were two important types in Europe called ‘Cataea’ and ‘Teutona’. They were made smooth and streamlined to fly better, but this had the knock-on effect of making them cut through the air much better, which was exploited to make a new class of striking weapons and so on.
These go back to the neolithic in Europe, I think I remember they found one in a cave in Poland which was 30,000 years old.
Apparently there was a version of the Cataea known to the Greeks
http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0063:id=cateia-cn