The proposal is to add another kind of object to the wallet database - a bitcoin address sans private key - which the client treats as if it were any other wallet adddress except for when it comes to signing and privkey export operations. This means RPC calls such as getreceivedbyaddress and listtransactions can be used on arbitrary bitcoin addresses.
I’ve added an RPC call:
0importaddress <bitcoinaddress> [label] [rescan=true]
The address is added as a new type of serialized object in wallet.dat and loads into the key maps of the CKeyStore instances with the key set to the CKeyID and the secret set to an empty vector.