The single core and poor ram to screen size ratio didn't hold back iOS 6 from the iPod Touch 4G.
That's a good point. Also, the iPhone 3GS got iOS 6 but the iPod touch 3G didn't, despite having identical internals. The difference was that the iPod touch was discontinued over two years earlier then the 3GS.
Apple made a lot of A5-powered devices over two years. Each device has the same amount of RAM, save the iPad 3, and the same CPU with minor variations in clock speed. Of these five devices, three of them remain for sale as of April 2014:
2011
- iPad 2
- iPad 3
- iPhone 4S
2012
- iPod touch 5G
- iPad mini
Technically speaking, nothing should stop Apple from updating all of these devices. They're all very similar from a spec standpoint. But we can safely assume the iPad 2 will be dropped given that Apple finally discontinued it. This is similar to last year, when Apple abruptly replaced the iPod touch 4G with a cheaper 5G model before WWDC. The iPad 3 is a wildcard; it has been discontinued since 2012, has already received two major iOS updates, and reportedly struggles under the demands of the Retina Display. Recent devices like the iPad 2 and iPhone 3GS have received three major updates each, so it's possible that Apple may give iOS 8 to the iPad 3. We'll find out for sure on June 2nd, but if I were an iPad 3 owner I wouldn't hold my breath.