> Dial-up modems reached their full 56kbps potential in 1997

That's simply not true. Modems were basically the same tech in the dsl era, and using light instead of electricity is a very gradual refinement.

> we're probably still far from the full potential of LLMs

Then how come the returns are so extremely diminishing?

> I don't see any obstacles to developing and switching to something better.

The obstacle is that it needs to be invented. There was nothing stopping newton from discovering relativity either. We simply have no idea what the road forward even looks like.