Releasing a 9.7" iPad in the spring and then another in the fall makes no sense. Releasing new products is a big investment of time, man power, and money, you know. They don't just pull them out of a hat. Why would they completely curtail the sales of the spring model for the sake of a fall model that couldn't possibly offer significant improvements?
If anything, with three active iPad lines I think we will see more staggered update cycles. We've already seen the Air 2 skip a 2015 upgrade, and given that the Mini 3 was only a superficial upgrade to the Mini 2, the Mini line in effect skipped a year too. There will definitely not be second 9.7" iPad in 2016. There may not even be another one until rather late in 2017.