What is the buy in to Scala from the team as a whole? What is the buy in for Java?
What is the level of expertise with Play?
What languages and frameworks has the team used previously on successful projects? What has it used on unsuccessful ones?
What matters more in this decision are the human factors, not the technology. That's why you're not considering Clojure among alternatives. If the team is split over language, that's a team problem and the solution can only come via working to get buy in from those who feel they have something to lose if Scala or java is the way forward.
Finally, if the long term goal is to transition from Java to Scala, Play with Java is a good first step. It gets Scala in the door, but keeps it out of the way as people are in the early stages of onboarding.
Comments
5-6 know Scala basics.
Where will the team get Scala expertise?
Where will it get Java expertise?
What is the buy in to Scala from the team as a whole? What is the buy in for Java?
What is the level of expertise with Play?
What languages and frameworks has the team used previously on successful projects? What has it used on unsuccessful ones?
What matters more in this decision are the human factors, not the technology. That's why you're not considering Clojure among alternatives. If the team is split over language, that's a team problem and the solution can only come via working to get buy in from those who feel they have something to lose if Scala or java is the way forward.
Finally, if the long term goal is to transition from Java to Scala, Play with Java is a good first step. It gets Scala in the door, but keeps it out of the way as people are in the early stages of onboarding.
Good luck.