Only one era of a nation is better, though I would still vastly prefer just a single era.
I would submit that the current preferences thread is biased however.
No doubt in the current format there will be a large spread of first nation picks across the eras which is an argument for the one nation mod. But I doubt in actuality there are that many people so fixated on a particular nation they would mind choosing another (or the same one in a different era).