Every instance I ever see of the Kopesh in either popular media or history it's always in context to Egypt and the bronze age but gets little recognition beyond that.
Was the Kopesh an impractical weapon or only really culturally significant to a specific time and place of history? Where most variations of ancient weapons were further developed and continued to be used hundreds of years from my novice research it doesn't seem like the kopesh did. Why?
The khopesh didn't spread over a huge area, but it wasn't just localised to Egypt. The earliest well-dated example I know of is Mesopotatian (Lagash, late 3rd millenium BC), and it's thought to have originated in Mesopotamia and spread to Egypt. They were used from Egypt through to Iran, over an area similar in extent to Western Europe (say, Iberia through to Germany). They were in use for over 1,000 years, from the later 3rd millenium through to the late 2nd millenium (and possibly the early 1st millenium, depending on what we are willing to call a "khopesh", such as this 9th century BC knife). This is similar to the time that the sabre (from the early Steppe sabres through to modern military sabres) has existed.
It was certainly a practical weapon, as seen by weapons of similar size and shape having evolved again. For example, the kopis and falcata are of similar size and weight, and have similarly curved cutting edges. Also, there are similar Indian swords, and the khukuri/kukri (which is often shorter and heavier). These weapons evolved independently from the khopesh, and can't be treated as Iron Age developments of the khopesh, but they still demonstrate the utility of the khopesh form.
However, being a practical weapon is not enough for a weapon to stay in use - there are many other practical weapons out there which can replace them. Replacement of one weapon by another might be for cost (the new one might be cheaper, and therefore better for mass armies, or the new one might be more expensive, and therefore better as a display of wealth), for fashion, or to suit different tactics. We don't know why the khopesh died out. It's linked to Egypt because it's prominent in Egyptian art as a symbol of royal power (in the New Kingdom, when it replaced the earlier mace as the iconic royal weapon). It was used as a soldier's weapon as well (just like the mace was both a common soldier's weapon and a royal symbol, and the sword in later years), but pharaohs, kings, and other VIPs are common subjects of art, and association with them makes the weapon more artistically visible.
A nice collection of photos/drawings and measurements can be seen at
http://myarmoury.com/talk/viewtopic.php?t=9497
From these, you can see that there was a significant amount of change and development within the khopesh family.
