Regarding json serialisation, at the time I was using scala, I found quite "unusual" that the play library could not deserialize a json with more than 26 fields (or something like that). I hope they fixed it in the newer versions, but still I don't get why to rewrite all the libs from scratch, when java has good ones available.
As asked (and answered) here[0], it used to be a Scala case class limitation. There are tricks to do it anyway, like manually mapping fields by writing your own JsReads or JsWrites for your object.
It was 22 fields and the problem was not serializing/deserializing, but it was a problem with the Scala functions and tuples system not supporting case classes with more than 21 fields. This limitation has been removed since Scala 2.11.
