@rphmeier 

/// A means of figuring out what outbound XCMP messages should be being sent.
pub trait XcmpMessageSource {
	/// Take a single XCMP message from the queue for the given `dest`, if one exists.
	fn take_outbound_messages(maximum_channels: usize) -> Vec<(ParaId, Vec<u8>)>;
}

I believe this trait not only should account for max messages taken from the storage, but also for segment limitations if we want to make this panic correct.
Probably primitives for segment should be extracted into common crate to be accessible from both pallets.

Originally posted by @slumber in #2438 (comment)