Spigen has 6S Plus cases on their site but I don't see any details listed such as size but they are listed as separate from 6 Plus cases so you maybe can assume 6 Plus won't fit 6S Plus. They have a Neo Hybird Carbon for S Plus but not for Plus.
I would have waited for confirmation on the 6S Plus size before buying cases.
Sent from my iPod touch using Tapatalk
That, or Spigen knows a bit about marketing. Even if their 6+ cases fit the 6s+ fine...they stand a chance of selling twice as many cases if they market them separately. And, until the new devices are released, they will sell lots in advance to people who reckon they will be different.
You're probably right about me acting prematurely on the cases & screen protector though. Won't be the first time I've been wrong...