I worry, slightly, admittedly, that this game will turn into another Empire: Total War and be an unfinished buggy P.O.S. that only seems to exist as an engine to get me to buy DLC.
But I don't think Firaxis will do it. More than likely, this is all Take-Two's idea, as publisher. Companies want to entice you to 1) buy off steam (they see a MUCH bigger profit off digital distribution than brick and mortar sales) and 2) spend more money than usual.
To do 1) they need to offer something as a bonus to get you to buy off Steam specifically (the Mesopotamia map.) This doesn't bug me. 2) is normally taken care of by deluxe editions: civ 4 had one, if you'll remember, came in a fancy box mostly.
The problem is, when you want to encourage hardcore fans to spend more than the common 50 dollars and still purchase online. So you have to add something of value, on some level, to an edition that can have no physical contents: and thus we have "special units" packs, "special armor" unlocks, and now "special civs". I don't agree with it, but I was going to buy the deluxe edition anyway. So it's really a small step for me. If this becomes an issue though? They won't get any money for it from me, not as a capable modder. If I want the Native Americans, I'll just find a still shot of Sitting Bull and do it myself.
Basically, you're still getting the 18 other civs they told you that you'd get. It's like being upset you no longer get toys in happy meals. Now, if they start rationing things french fry by french fry, you have something to worry about.