Some new Xamarin (but experienced iOS native) devs, like this one https://twitter.com/azamsharp/status/915391382377959424, start using Xamarin by creating a new project and opening the storyboard in Xcode to make some UI changes. It's probably not surprising that iOS native devs would do that.
And then this user at least tried to build the project in XCode, seeing the confusing message "Invalid iOS deployment version..." (see Twitter link above for full message).
Clearly this user didn't understand the expected workflow, that you aren't supposed to build in Xcode, but this message caused them to think the whole experience was broken (and spread that message to their Twitter followers).
We should instead have the xcodeproj we create output an user friendly message for the build that educates the user on the expected workflow here. Something like:
"This is a stub project for Storyboard editing. Don't build it in XCode. Instead make your UI changes, save them, and go back to Visual Studio to build and run your project there."
It can be a custom build step, with an echo of the message and an exit 1 or something like that, to fail the build.
So I'm not sure we can hack the .xcodeproj to generate custom build errors (something to look into).
However we could (and maybe should) certainly show the user an alert (tutorial style) the first time they try to open a storyboard in Xcode (show that only once).
This would let us explain what our "open storyboard in Xcode" story is about (maybe link to some documentation.
We could explain the limits: it's a generated project that can have build errors (but it doesn't really matter because we'll be able to import the changes to VSMac anyway).
We could also promote our iOS designer there and explain its great features (that Xcode doesn't have), mostly that it removes this complex drag and drop concept with outlets.
Anything that PM and docs think we should mention.