Many developers aren't interested to Apple's "new fluffy colorful things" but the web browser improvements. Here is an unofficial list about what has changed in Safari on iOS8 (*).

So let's do some benchmarks, to test WebGL performance and the rest.

Web standard support: html5test

Score: 438

The most known benchmark to test the current web possibilities.

http://html5test.com

WebGL 3D performance: aquarium



Fps: 20 (with 10 fishes)

A simple WebGL demo by Google, the newer iPad should have much better results

https://webglsamples.googlecode.com/hg/aquarium/aquarium.html

Canvas 2D performance: fishbowl

Fps: 9 (with 250 fishes and water/sound disabled)

This is a demo from Microsoft

http://ie.microsoft.com/testdrive/performance/fishbowl/

General javascript performance: v8 v5

score: 1316 (it's increased of ~100points after the upgrade from iOS 7.1 )

The v8 benchmark is old and it works everywhere, the new Octane 2 and 1 crashed on iOS8 on iPad2.

http://v8.googlecode.com/svn/data/benchmarks/v5/run.html

In conclusion I can say that the web stuff has improved in iOS 8 but if you have other tablets please share your results in the comment!

(*) Personally I don't see the "upload bug" because I can upload files via web browser on iOS 8.