Emblems are intended for that level of content, and there likely won't be new rewards trickling down. I actually like this system better; raiding Naxx every week won't be "mandatory" the way that raiding Kara was.

So, from this one sentence, we can derive that there will be an Emblem for each tier of content:

Thus maintaining the steady progression of both 10 and 25-man raiding, and also sticking with their stated design objective that managing twenty-five players in a raid should yield higher rewards than managing ten.

This also eliminates any save/spend strategy regarding emblems, which is probably for the best anyway. If you see something you like at that tier, grab it.