I don't remember the exact sources from which I heard about the new movie plans (only plans, it's not in production or anything yet). But it was from Austrian people, apparently Vienna has been full of these rumours, and someone who should know (I don't remember who) had said in a public event that it indeed is being planned. I also read about it in some Austrian newspaper. If I come across quotable sources again, I'll let you know.
Catherine is a good actress, but she's just not physically the Sisi type at all. Just because they're both beautiful and dark-haired doesn't mean that they're alike. And I don't think Catherine would work as the middle-aged Elisabeth simply because she is too healthy. She has a normal-sized feminine figure, at least the last time I saw something with her in it, and the way Sisi worked out and near starved herself in order to keep excessively slim wouldn't be able to come out.
Yes, the musical is coming to Belgium in the near future. It is also currently playing in Zurich (the German tour moved there after Berlin) and it's in the repertoire of the Budapest Operetta Theatre, though they haven't had performances of it for a few months now. But probably they will at some point.
Was it the Vienna DVD of the musical with Maya Hakvoort and Máté Kamarás you watched, Imperial Grounds? Not that there is any other version officially (besides the Takarazuka DVDs from Japan, but they're a bit different), but there is all sorts of stuff in circulation. The Vienna production is my biggest favourite, along with the Hungarian one.