Fun speculation by Graham Spencer over at MacStories:

Because my mind was a bit fuzzy on the historical iPhone lineups (particularly the early years), I decided to go back and make a graph to simply and clearly show what Apple has done in the past. The dates I used were based on when each iPhone was available in the US (not the announcement date). Tier 1 represents the newest and most advanced iPhone available at the time. Although there are slight differences between the iPhone 6 and iPhone 6 Plus, they are largely identical (both have an A8 processor with 1 GB RAM, etc) and as a result I’ve characterised them both as Tier 1. Tier 2 represents the next best iPhone available (often the previous year’s Tier 1 model) and Tier 3 is the next best again.

There’s no doubt one of his options will be correct. As for which one, I’m going to say Option 1A (Tier 1: iPhone 6s, 6s Plus. Tier 2: iPhone. Tier 3: iPhone 5s). I don’t think we’ll be seeing a plastic iPhone 6c, much less an iPhone 6c Plus. I’d love to see Option 2A, with Apple releasing a 4-inch iPhone 6s (Mini?) alongside the 4.7-inch and 5.5-inch models, but I’m not getting my hopes up.