Time to speculate.
Part of the decision to purchase a mobile device is based on the support you expect to receive in the future. Apple just announced a new/updated 16Gig iPod Touch with two cameras. The question is, will this new iPod Touch run the new iOS 9 next year? If so, could anything possibly prevent the older iPod Touch 5s from also running iOS 9? Will any iOS devices with the A5 CPU or higher be able to run iOS 9 next year?
What do you think Apple will do?
Any iOS device announced this year will run iOS 9 next year. While not a definite, I'd bet quite a lot on it. So, if there's a new iPod touch this year, it's a safe bet that it'll take iOS 9. As for the fifth generation iPod touch, I'd bet that all A5 devices will be left out of iOS 9, with the third generation iPad going either way (given its 1GB of RAM on the A5X versus the 512MB on the A5 devices).