This is a withdrawn posting.
There is a shortage of wrappers publically available for some of the popular languages (php, go, python, ruby) when it comes to interacting with zcash via the publically documented RPC calls.
When others have the time to pitch up and create them, the payment providers listed https://help.shopify.com/manual/payments/alternative-payments/bitcoin which take care of all things bitcoin for shopify would likely start the integration process.
Wait, reading that back, I sound like an optimist.
What I meant to say is, when the market cap, followed by transaction count reaches similar heights to bitcoin when those providers took notice and provided a solution, only then may we see this method become available.