I don't imagine the lighthing. Maybe we are creating a lot of expectatives and it could be quite simple as Vancouver did.
Can you imagine a "better" version of the lighting in Shenzhen for the Universiade FISU Games in 2011 when they set on fire the athtetic track and the fire went on till the cauldron??
I don't like the idea of a "internal" cauldron, since Olympics have to be share with everyone (Indeed, the motto is "Everyone's London 2012", so it would be counterproductive)
Remember the "selfish" cauldron in Seoul??? No man!!!!
The idea of a second or external cauldron, as in Vancouver, pleased me a lot!!!!
Not only Vancouver had a external cauldron, remember in Doha for the Asian Games, the astrolabe internal caludron and the external one in the tower next to the Califa Stadium.
During the Panamerican Games in Guadalajara, Mexico there was a second cauldron in the track field at Telmex Athletic Stadium. It was a exact copy of the "official one" which was set up on the Omnilfe Stadium's roof..