Except most household have more than 1 person. A family of four sharing 100Mbps isn't a lot.
I am not sure if 100Mbps upload is a realistic option in US. But I would at least expect 50Mbps to be minimum per household. DOSCIS 4.0 should be able to handle that.
DOCSIS 4.0 was ( finally ) finalised last year. And could be pushed for upgrading. But that is just the last mile, Cable companies will still have to ensure fibre roll out. Look at UK. They had a half decent infrastructure with DSL and could have pushed G.Fast, instead they just bite the bullet and pushed FTTP to maximum.
Although technically I was only upgraded from 100 to 200 for free a few years ago because a competitor came in since then with fiber who offers 200/200 at the same price. I haven't switched over because they cut me a deal and truthfully I don't upload enough for the extra amount to matter and I get single digit ping times out of my provider which I'm happy with.