Wow! This saved my day! How did you figure this out? I couldn't have doen that in a million years.

Here's a new update. I have three subscriptions and I added intro offers to two of them on Monday. About 10 minutes ago, I can finally see the offer price taking effect on production devices. So it just takes really really long time for introductory prices to take effect on production devices, for my app at least! About 36 hours ago, I added an introductory price to my third subscription just for the purpose of testing, and it still hasn't taken effect now. I'll keep you posted on how long it finally takes effect. Here's the case number for my previous contact with Apple: 101708089810. I'd be glad to provide any further information and help with testing or anything, as I think this is quite important for a lot of developers.