This would address one of our bigger criticisms of iOS 8, which in our testing was significantly slower on these older devices than iOS 7 was. Apps took longer to launch, and the user interface was often jerky and inconsistent in ways that it wasn't before. Apple has a long history of speeding up new iOS versions on old hardware post-release—iOS 4.1 on the iPhone 3G, iOS 7.1 on the iPhone 4, and now iOS 8.1.1. It would be nice if performance on older hardware was better optimized in the first place, but newer hardware obviously takes precedence.
When the final version of iOS 8.1.1 is released, we'll throw it on an iPhone 4S and iPad 2 to see how much the performance really improves. Although they're not mentioned by name in the release notes, we'd also expect the improvements to help the original iPad Mini and the fifth-generation iPod Touch, which are internally similar to the 4S and iPad 2.