If the past updates are anything to go by we won't be getting Amber and GDR2 as separate updates. That would cost too much for MS and Nokia. It makes much more common sense for MS and Nokia to work together to provide an update that will roll both into one package, delivered to the customer. Of course there are phones that aren't Nokia, so MS will deliver a separate build to them without the 'Amber' things. These builds will be internally tested and tweaked before being delivered to the carriers, who again test them extensively. Once everything is given the go-ahead that's when the carriers start rolling out the updates to our phones. Typically those with contracts will get the updates first (updates tend to be rolled out over a period of 28 days with more and more IMEI numbers being 'unlocked' to receive the update every day, this is to make sure the servers aren't broken by requests to update.
At least this is how I think it works...