Our MMO sample has two parts one is Server Side and the other one is Client Side. The server side coding has been done in Java and the client side was made using Unity. So, even if you are making your game in Swift, the same server side code will work. For the client side, you can take the reference of Unity Client code.
As your game is an MMO, so combining the location of players in a single chunk may not be a good option as there is a imit on message size which a client can send or recieve.
As you said, you may consider Unity to make your game going further, in that case you dont need to convert the Client side code of the sample to Swift to get started.
Let me know if you have any further queries.