There is a very large side effect to delaying 2.1

If it was released at lunch or shortly after than things like crystal tower with ilvl 80 gear and dungeon hard modes would make sense. They would close the gap between easy content and coil. However by December average person will have 3 months worth of mythology tomes, relic +1 and probably at least something from coil. What would be the point of new content in 2.1? It will be obsolete at that time.