https://github.com/nextime/eshop-bitpay-mg
This is a fairly easy plugin based on the example plugin from the eshop web site. It uses the "hosted checkout" method on Bitpay, and it doesn't NOT manage IPN calls, anyway, at least now i have an integrated bitpay support in the checkout procedure on my own eshop based wordpress e-commerce.
To use it, just go to bitpay, login with your account, and create a checkout button. You will need to go in the wordpress eshop admin interface and setup your email, your currency of choice and the "button data" bitpay will give when you create your checkout button. That's it.