Basically if you look at what people use text for online it usually isn't anything serious, even these discussions don't have all that much gravity and HN is probably the most serious site I've seen.
Text also has less emotion and involvement attached and I think a lot of people won't connect with a text based system like this or won't feel comfortable contributing.
An idea for a way to feed peoples passions would be some kind of automatically generated video conference setup to split people into random think tank groups based on availability for each policy they indicate they want to be part of. Then perhaps one person, presumable someone that indicates they feel comfortable writing could contribute on behalf of their group to the text based policy page.