I don't know if it will be with a "minor" refresh, but 8GB will be standard sooner than later, if for no other reason than market pressure, and the cost difference won't make sense to deal with so many configurations when 16GB becomes an option.
Some folks around here are so caught up with whether 4GB is enough technically, that they ignore the larger marketplace. Apple doesn't get too caught up in the specs race, but it can't completely ignore it either - even most lower end computers come with 8GB now, especially in the US$1,000 range. Just a quick look at Dell, and almost all of their computers over $600 come with 8GB.