I realize that this is very unlikely to happen, but part of me wishes you could transfer characters from Classic to BfA. I always find the lore jarring when leveling one of the initial 8 races through Cataclysm lore, then going to Outland and Northrend. It would be cool to level up in Classic then transfer to BfA once I got to 60. I'd put the likelihood of this happening at less than 1% though.