Just because the devs won't be actively patching stuff doesn't mean it's pointless. Loads of feedback and date is gathered during the time they are on vacation, and when they return they wont really be behind compared to of they waited until they could devote their fully attention to it.
At worst players will find some gamebreaking bug that won't be fixed until next year, but honestly who really cares. It's the PTR, and either we get something, or we get nothing.
I will happily take something that has a chance of being broken than nothing when it comes to PTR.