OK, I thought maybe the Communion Chapel was something special I had missed.
I think you have to see what is involved here. There are some modern churches that have the Blessed Sacrament in a box in the back room or sometimes, strangely enough, near the door. And they also have no altars - there is a table with the bizarre "presider's chair" behind it. Obviously the Blessed Sacrament cannot go there (and he does mention this issue of the chair), so he is telling bishops what they should do in this circumstance.
In terms of cathedrals, the Blessed Sacrament has frequently been in a side chapel because (a) European cathedrals often had the choir (an enclosed area with choir stalls for the cathedral clergy) front and center and (b) cathedrals were busy places and it was considered more reverent to construct a special chapel.
Please go back and read the section that says "What this document is," or something to that effect. It's in the preamble. The document was a response to questions asked by various bishops at an event many months ago. What it does is lay groundwork for specific implementations. And BXVI, instead of just responding to these things in a shotgun fashion, ties it all together around the Eucharist.
I think this was essentially a matter of telling the bishops the basic rules. The next step will be inidividual enforcement, which I think will happen, although with BXVI it will be very subtle and not the dramatic clap of thunder we would all like to see.
fair enough.