I don't get why people suggest this. Why should someone buy another tablet when they want to be able to see two things at once. You don't necessarily even need to be able to interact with both apps at once, just see them.
I also don't get the argument of 'buy another tablet then'. Well...you could but then lose the App store. Why is it bad wanting something more from the device? I don't particularly care eitherway. It would be nice if Apple would implement it, but its going to happen for jailbroken devices one way or another. It already has (twice) if you count the buggy implementations.
Regardless of what anyone says, if a pro/larger tablet is coming, then so is split-screen/multitasking. It would be a complete waste not to. Eventually its going too, there is only so long that the ipad can survive with a mobile phone OS, or any tablet for that matter.