I don't think there was some planned 6.3 that was scrapped. I think WoD was just planned as one year expansion. Then they realized you can't just put more people to work on expansion and get it done faster. There are bottlenecks during expansion development.
Of course many stuff were cut from this expac, so who knows. But as I said in previous post, we had rumors that WoD will have just 2 tiers even before it launched.