Dropping everything with less than 2GB or RAM / Apple A12 is definitely possible.
There is absolutely no chance iOS/iPad OS 16 will require A12 or even A11 and higher.The concerning aspect is dropping the A10 in the ipod touch. Apple has done this in the past where they discontinued a model just ahead of WWDC that dropped support for that device (iPod 4 before iOS7 WWDC). They have also dropped two generations worth of devices in a single year too (e.g. iPad 2 and 3 were dropped together, iphone 6/plus and 5S were dropped together in 13)
iOS16 could be A11 and higher
Also, it seems to me that the iPod touch can be ignored, based on Apple's usual support practices. It's like they don't factor that device at all in their support decision making.
As for the iPhone 6, aside from a low cost 32 GB version, it was discontinued in 2016 at the same time as the iPhone 5S, so it's not a major surprise the 5S and 6 lost support at the same time.