The new iPhone 6 and 6+ have both been tested and rank among the fastest smartphones available. The same is expected to be true of the new iPads.
Besides an issue with page reloading tabs (of which it is in no way certain that it is attributable to a lack of RAM) there have been no wide-publicised issues with a lack of RAM for any application on iOS that I'm aware of.
So what are you talking about? In what way would 4 Gb RAM make the iPad any faster or better performing? In stead of just repeating the same "we need more RAM" mantra, I would really like to have some insight into what people are missing here.
The current iPad Air is only a kick away from the iPhone 6 and 6 Plus on Geekbench. While only benchmarks it's clear the issue with iOS 8 on the current iPad Air is down to poor optimisation. 8.1 is better than 8.0.2 but there's still plenty of improvement to be made before it reaches iOS 7 levels of smoothness.
It's only in beta 2 so hopefully there's still time for more tweaking.