If Apple is considering making that move anyway why not put the Atom processor in it as soon as 22nm is ready? It can be ready six months to a year faster than TSMC can have a reliable supply of their 28nm. -----
As a side:
The companies said they moved the test chip design from RTL to "tape-out" in six months, usuing a design flow co-ordinated by TSMC. The companies did not state how long the design would take to be instantiated successfully in 20-nm silicon, which at TSMC is a planar process.