Thanks, Kathryn, for going out on a limb to present your view. And you’re right that it will draw fire from both sides, but you should be used to that by now. 
Since you indicated an openness to changing your mind, rather than engaging in debate about ad hoc Adam, I’d actually like to discuss your views.
“All Evolutionary Creationists agree that the scientific evidence indicates that the human population has never dipped below a few thousand within the last 200,000 years.”
I think you can extend that to 500-700,000 years, unless what you’re saying is that the population of H. sapiens has never dipped below a few thousand, in which case you can probably extend it to at least 300,000 years to correspond to the date of the Jebel Irhoud fossil.
I prefer to believe that Adam and Eve were a real couple in history who lived in Mesopotamia, among a larger population of people, perhaps around 6,000 B.C. … Thriving cities existed when Adam and Eve lived. Art, trade, tools, language, and farming were familiar to their contemporaries. … In the fullness of time, God called two people, Adam and Eve, into a special covenantal relationship with himself, and into a one-flesh unity with each other.
Let’s take these one by one. Around 6000 B.C., Mesopotamia was likely the most populous place on Earth. You mention a thriving culture already in existence when Adam and Eve were called into covenantal relationship with God. However, this misses the point of Gen. 4.17-25, which is to show ordinary people as imago Dei founding cities and advancing culture. This is a deliberate contrast with Mesopotamian ideology, which gave the king, as imago Dei, the sole credit and responsibility for cultural advancement. (See Middleton, The Liberating Image.) Furthermore, by 6000 B.C. people already had been living in tents, raising livestock, and playing stringed instruments and pipes (4.20-21) for thousands of years, although working bronze and iron were still a few thousand years away. If you want to consider this portion of Genesis as historical narrative, then the history is wrong whether you date it 200,000 years ago or 6,000 years ago.
On the “special covenantal relationship,” where do you see evidence of a covenant in Gen. 2-3? Honestly, I am (mostly) Reformed in my theology, but if there is a covenant between God and “the man” in the garden, I see no evidence of it. Personally, I think covenant theologians wished it into existence just to make everything nice and symmetrical. haha.
On the “one-flesh unity,” this creates even bigger historical headaches than the cultural advances of Genesis 4. Marriage, as a social contract, existed long before 6000 B.C. In fact, Terrence Deacon proposes in The Symbolic Species that “marriage” – understood as a social contract regulating sex in multi-male/multi-female groups – was one of the driving forces in the evolution of human sociality and symbolic reference. Another way of putting this is that “marriage” has been a feature of human culture since the dawn of mankind, which is where Genesis 2 locates it. Marriage was not instituted by God in 6000 B.C.
They were selves, free to obey or rebel. He gave them rules and consequences for breaking those rules. And they chose, in their freedom, to rebel. Whether or not there was an actual piece of fruit involved is interesting but beside the point: they were after what it represented—knowledge of good and evil.
How do you define “knowledge of good and evil”? What knowledge did Adam and Eve gain that their contemporaries in 6000 B.C. did not possess, other than knowledge of God?
One reason I don’t believe Adam and Eve were the sole progenitors of all humanity is because the Bible itself gives hints that there were other people around when Adam and Eve lived.
Try this one on for size: If ha’adam is a literary archetype, then “the man” represents both the individual and all of mankind, so of course there were other people around! All of humanity is taken up in the symbol.