I remember initially struggling with the stuff in ML in the first year at university, I got it but I and many others had an initial struggle. I think that at least for beginners and maybe those coming from runtime duck typed languages Python, PHP, Ruby etc. it will be more of a barrier than you think.
For #1 in Objective C you inherit from NSObject (or a subclass thereof) for every class anyway so it is in all the examples and it isn't something that you need to do especially for a protocol.
For #2 yes of course you can have an array of a generic type but firstly you need to understand enough about the type system to create your array in that form and secondly what you get out will <AnyType> objects rather than <id>'s which get automatically cast to whatever you assign them to. But I do like the idiom for downcasting using as?:
if let movie = item as? Movie {
println("Movie: '\(movie.name)', dir. \(movie.director)")
} else if let song = item as? Song {
println("Song: '\(song.name)', by \(song.artist)")
}
For #2 you are flat out incorrect. Swift arrays can be containers of AnyType, in which case they interoperate perfectly with NSArray, and this is the default behavior when working with Cocoa.
Your fear about type related complexity being a real issue seems not to be justified by your examples.
Compared to dealing with the C based fragility of Objective-C, Swift is simply better for anything that it can do.