I doubt a law firm would be happy for its legal opinions to be published. Restrictions the number of people that might rely on them seems likely to be in default terms and conditions. While defaults can be changed I see little reason in this case in the short term.

What Manifold is doing seems to me to be substantially different from what I think is the common understanding of what a sweepstake is. Perhaps in at least a couple of different ways. per https://manifold.markets/ChristopherRandles/what-distinguishes-sweepstakes-from