Can I release Swift implementation of an application over the Xamarin implementation in Apple store? I developed an application that is currently implemented using Xamarin.iOS.
I've come to a point where I think it's better to rewrite my app using Swift.

My question is, can I release the application rewritten in Swift as a major update of the current application? Is Apple store capable of upgrading the app even if one implementation is written in Xamarin.iOS and the other one in Swift?
Sure - the store delivers binary content that it code signs as complete so it doesn’t matter how you got the submission to Apple. 

Now, the end user experience could still be a mess if you don’t have a smooth migration plan for app data, settings and what happens when someone restores a backup from 6 months ago onto the new version of the app. Those things are hard to test, possibly difficult to program and not something that was designed into your data model currently.