I have just ported Paul Slot's awesome "PSCustomViewFromXib" from objective C to Swift

CustomViewFromXib.swift

// Inspired by Paul Slot's awesome PSCustomViewFromXib, https://github.com/PaulSolt/CustomUIView
class CustomViewFromXib: UIView {
	var customView: UIView?
	
	override init(frame: CGRect) {
		super.init(frame: frame)

		let className = String(self.dynamicType)
		let anyObjectOrNil: AnyObject? = NSBundle.mainBundle().loadNibNamed(className, owner: self, options: nil)?.first
		guard let anyObject = anyObjectOrNil else {
			print("ERROR: CustomViewFromXib.init(frame:) Expected customView to be non-nil, but got nil")
			return
		}
		
		guard let customView = anyObject as? UIView else {
			let classNameForAnyObject = String(anyObject.dynamicType)
			print("ERROR: CustomViewFromXib.init(frame:) Expected customView to be a UIView, but got: \(classNameForAnyObject)")
			return
		}
		self.customView = customView
		customView.frame = self.bounds
		
		if CGRectIsEmpty(frame) {
			self.bounds = customView.bounds
		}
		
		addSubview(customView)
	}

	required init?(coder aDecoder: NSCoder) {
	    fatalError("init(coder:) has not been implemented")
	}
}

Awesome!

Ported to Xcode8.3.1 and swift3.1

class CustomViewFromXib: UIView {
	var customView: UIView?
	
	override init(frame: CGRect) {
		super.init(frame: frame)
		
		let className = String(describing: type(of: self))
		let topLevelObjects: [Any]? = Bundle.main.loadNibNamed(className, owner: self, options: nil)
		guard let topLevelObject = topLevelObjects?.first else {
			print("ERROR: CustomViewFromXib.init(frame:) Expected topLevelObject to be non-nil, but got nil")
			return
		}
		
		guard let customView = topLevelObject as? UIView else {
			let classNameForTopLevelObject = String(describing: type(of: topLevelObject))
			print("ERROR: CustomViewFromXib.init(frame:) Expected customView to be a UIView, but got: \(classNameForTopLevelObject)")
			return
		}
		self.customView = customView
		customView.frame = self.bounds
		
		if frame.isEmpty {
			self.bounds = customView.bounds
		}
		
		addSubview(customView)
	}
	
	required init?(coder aDecoder: NSCoder) {
		fatalError("init(coder:) has not been implemented")
	}
}

class CustomViewFromXib: UIView {
	var customView: UIView?
	
	override init(frame: CGRect) {
		super.init(frame: frame)
		
		let nibName = String(describing: type(of: self))
		let customView: UIView = Bundle.loadView(fromNib: nibName, withType: UIView.self)
		self.customView = customView
		customView.frame = self.bounds
		
		if frame.isEmpty {
			self.bounds = customView.bounds
		}
		
		addSubview(customView)
	}
	
	required init?(coder aDecoder: NSCoder) {
		fatalError("init(coder:) has not been implemented")
	}
}

extension Bundle {
	static func loadView<T>(fromNib name: String, withType typeId: T.Type) -> T {
		guard let view = Bundle.main.loadNibNamed(name, owner: nil, options: nil)?.first as? T else {
			fatalError("Could not load view with type \(type(of: typeId))")
		}
		return view
	}
}

Is this something that you could create a pull-request and wrap up into: CustomUIView with a Swift version of the project?