I do not think Apple reached its peak in a strict sense.
But if the recent sales slowed down, which is quite possible, it may be an indication of the smartphone market reaching its peak, and Apple is the first one to feel it. Any smartphone, regardless of the platform or brands, they work essentially the same way, communication, PIM, Internet, and contents consumption etc. When the industry continues this way, at some point, it will hit the peak albeit perhaps gradually.
When this happens, I assume the market will get into war of hardware features and price.
Someone has to break the mould and change the way the people (we) perceive and use the mobile terminal.
If anyone should even think about it, it must be Apple. Hope they are working on something revolutionary, the way they introduced the iPhone back in 2007. A fantasy