It used to be the law that touring acts MUST have at least one local support act. Not so anymore.
So U2 had, for example, the one song Sidewinder for Popmart, and even though they had B.A.D. imported for ZooTV, they also had Kim Salmon up first. Not exactly stellar choices, and almost certainly record company, not U2, choices. So, even if that law were still in place, you'd probably still get Jay Z, just with some currently promoted Universal hoisted act on first. That could be okay, or could be complete rubbish. And if you are looking at larger local bands, Australian rock is in a pretty bad place at the moment. Wolfmother? Jet? Come on. They're awful.
If that law were still in place, I think it would be cool to have an electronic act on first (a genre where Australia is actually world class), then you have hip hop, then you have rock. You get a mini festival! I've never understood why people think a U2 support slot should be for rock acts only. That's absolutely ridiculous. Only rule is that they should be somewhat lively. It's a warm up slot. No matter what genre they are, it should be something with a bit of energy.
I'm not much of a Kanye fan, but I thought he deserved points for effort. He was trying really hard to win the crowd over, and I think Jay Z will fare far better than Kanye in terms of audience response. It's a decent booking. It adds massive hype to the tour. Don't for a second think that the U2 + Jay Z = Negative crowd will outnumber the U2 & Jay Z = Huge Event crowd.
And yeah, as someone else said, could be worse - could be Snow Patrol!