I certainly think it's within the realm of possibilities that an Amero could be in the works or even planned for.
To say it's outside the realm of possibilities, given the pattern that we see (the parallels between the events and treaties and agreements leading up to the EU and the desire for a North American Community) now, in this continent, I think one would be foolish to dismiss this outright.
I'm assuming you've not read this informative article:
The EU and the NAU ~ Two Peas In A Pod!
By Daneen G. Peterson, Ph.D.
May 20, 2007
Updated August 31, 2007
Except the EU exists and the NAU does not.