Lets consider a smaller part of the picture, just Asia Pacific. They use maybe 6 data centres in the APNIC area, all using the one public ASN from APNIC. The data centres do not have a common carrier/connectivity between them. A couple of sites are connected via VPN, 2 or 3 are connected with one carrier and the others with a different carrier again. Most sites have more than one link to other sites for redundancy. All links are either layer 2, or point to point layer 3. Most sites have 3 or 4 BPG devices in them, all in the same AS.
Creating a full iBGP mesh within a singe data centre is ok. But I have had to use a lot of route reflectors to build the connectivity between the different data centres.
I have never used a BGP Confederation before, but I am starting to think this will be the most manageable way. Make each datacentre a a separate sub-AS, because I can easily create a full mesh within a data centre. Then peering between the sub-AS's will become trivial, while still providing the appearance of a single AS to all the external peers.
Have you use BGP Confederation before? Had a good/bad experience?
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