Will coinbase.com have replay protection for receives? According to this, "Bitcoin Segwit2x does not have any built-in replay protection, but Coinbase has implemented our own replay protection system. You can safely send any BTC or B2X from Coinbase without worrying about replays on the other chain."

But will they have any replay protection for receives, as well as sends? I don't imagine they can do anything to prevent a transaction sent to them from being replayed on both chains, but at least they could detect the replay, and credit both currencies to your account.

I'll probably try to avoid this, but just wondering if I have some backup protection if I make a mistake.
It is impossible for the receiver of a transaction to prevent transaction replay of the transaction. They cannot do anything to that transaction to make it unreplayable.

However it is likely that Coinbase will credit both your Bitcoin and Segwit2x if a transaction is replayed. This is because they should be operating nodes for Bitcoin and nodes for Segwit2x which will inform their backend of the transactions occurring on each chain. Since a replayed transaction will be seen on both chains, both nodes will see it and thus their backend will credit your accounts.