Using segwit and creating Pay-To-Witness (P2WPKH) addresses I'm going through this guide: https://bitcoincore.org/en/segwit_wallet_dev/

I might be understanding this incorrectly, but it sounds like the users and/or wallet custodian (coinbase, blockchain.info, etc) must create P2SH-P2WPKH addresses in order for the witness data to be segregated and save on block space.  According to the guide, soon after activation only a limited number of segwit transactions will be on the network. 

Does the new release 0.13.1 default to creating P2WPKH addresses or will the users and online wallet providers have to do this manually?  Will there be a built-in RPC function for creating these addresses similar to createmultisig ?
I might be understanding this incorrectly, but it sounds like the users and/or wallet custodian (coinbase, blockchain.info, etc) must create a P2SH-P2WPKH addresses in order for the witness data to be segregated and save on block space.


Correct, you first have to receive money to a SegWit address. Witness space can only be used when spending outputs received on a SegWit address. The bitcoins can be sent to any type of address from a SegWit input, though.


  Does the new release 0.13.1 default to creating P2WPKH addresses or will the users and online wallet providers have to do this manually? Will there be a built-in RPC function for creating these addresses similar to createmultisig ?


SegWit transactions created before the activation of SegWit could lead to permanent loss of funds, therefore, 0.13.1 will not create SegWit addresses or transactions by default.

→ Please consider the section Upgrade Safety in Bitcoin Core's SegWit Wallet Developer Guide carefully.