That's quite a big one-man-project! But if you manage to create such a wallet for iOS, you'd probably can easily sell it for a few $ inside of the app store.
I believe there are quite some people who'd love to have such a fully functional wallet for their iOS device. I, personally, wouldn't mind paying a few dollars for a nice-looking fully functional mobile wallet (especially if there is no good wallet available).
IMO you'd deserve a few dollars per download.
It will be 100 % free to use, I will start working on it in 2019
Anyway, you can try to use a simulator like iAndroid where you can install android apps/electrum, just found a source while searching for android emulator from here https://tricksempire.com/iandroid-android-simulator-iphone-ipad-ios/
I don't know how safe it is to use but since, you are planning to make a watch only wallet this might be a good alternative solution.