What will a "license" for LT then include?
But making money from open source projects is hard enough, and varied enough, that it makes sense to spend a lot of time thinking about and experimenting with this one before committing to anything. It looks like that's what they're doing. So I don't think there will be a firm answer to this until they're much closer to launch -- or that it would be a good idea to offer one.
Mass adoption, patches, test cases, design, feedback and money comes only when it reaches crazy adoption and a lot of people hack on it.
That is why it is important for LightTable to release a minimal usable version ASAP and then improve it in further releases.
All this needs a open source set up. A Cathedral set up earlier but a bazaar set up later.
Going for YC is clearly a great starting point for building a scalable business, so I wonder what the business logic will look like. As in genuinely, positively interested to know. :-)