Is core planning on integrating Segwit2x?
No.
If no, what exactly is core planning in regards to a BIP148 chain split or a Segwit2x hard fork, if anything?
Nothing. Many of the Core developers believe that both BIP 148 and Segwit2x will fail. In the event of a chain split, there will be an alert posted on bitcoin.org (there's going to be one anyways because of the possibility of a chain split) with instructions on how to make your node follow the chain you want it to follow. It's very easy to do by using the
invalidateblock RPC command.