Hello Hakan,
My Iyzico payment extension is not yet ready at all, and currently I do not have any plans to finish it, because now I have more profitable projects (implementing and improving my other Magento 2 extensions).
I can finish it on the terms of my custom payment gateway integration service.
Of course, it will include the installment and card storage features.
Such features are already implemented in my other payment extensions.
You can see the installment feature in action in my 歐付寶 allPay Taiwanese payment extension.
You can see the card storage feature in action in the following my payment extensions: