It always seemed as though the big obstacle would be political. Hah! I say to technological difficulties. People are good at solving that sort of thing. And raising money to do something that huge is something I'm brushing away to get to what I believe would be the true pain in the ass. Any particular big engineering solution will affect different regions in different ways, and that's politics. Politics are hard.
However, before we can even begin to address the politics, we'd have to know something about how different regions would be affected, and we aren't even close to knowing enough for that. So, my random question of the day is "What would we need to know to have a good idea of the detailed effects of a proposed big climate engineering project?"