waiting for OP to cite source for his speculation. I google "BMW 5 Wagon for USA" almost once a month looking for something new on this issue and keep seeing the same stuff from years ago. I have not read or seen anything new on this. But there is always hope.
Seems unlikely they would use the LCI as an excuse to get back into the US market and spend all the money to federalize (ie crash test etc) the F11 for the USA and Canada. Having said that, I would LOVE to be proved wrong on the issue.
They are a lovely car and I have seen them in the flesh here.