I think it would be prudent for me to jump in here, for I actually founded a region with an Open Assembly:
Cynosure. As such, for those who are considering other NS regions with Open Assemblies, Cynosure is a growing one that is using it rather successfully, and I'll write a case study using this region below.
When I founded the region, I designed the Constitution to specifically lay out exactly how the Open Assembly (which Cynosure calls the Senate) would work. While it probably would be set out differently in Wintreath, it has worked rather successfully for Cynosure.
Citizen's can apply to become a member of the Senate, and those that do instantly gain access, providing they have been in the region for two weeks. They can also gain access prior to this two week probation with support of the Senate Manager (equivalent to the Speaker) or the Councillor (equivalent to the Monarch). This separates the citizens into two camps; those interested in participating in the legal side of the region, and those not. As Cynosure is primarily a roleplay region, the majority of citizens simply come on to roleplay rather than participate in law, so the Senate contains a subset of citizens.
The Senate specifically has three phases when passing law. Phase 1: Proposal Phase, involves Senators proposing an act with the idea of getting two co-sponsors to move it into the main body of the Senate. This is to ensure that the basis of the law is sound and has at least a small support.
Phase 2: Debate Phase, lasts a minimum of three days. During this phase, Senator's register on the act by motioning to either vote, hold or table. The Sponsors (the three Senators who introduced the act) are automatically considered registered and need to motion to move things forward. This is important, because when there is a 100% motion to vote of all registered senators after the three day minimum period, the vote automatically moves to a vote by, and only those who are registered on an act are eligible to vote on it.
Phase 3: Vote Phase, lasts four days or until everyone has voted enough to make it pass. The Senate requires 2/3 approval of all registered voters. The idea behind registration is that it further cuts down the size of the Senate to allow only those interested in a particular act to vote on it.
Now, that's the basics, and I suspect in Wintreath's case it'll work completely differently. My point here is not to bring this phased approach over to our Open Assembly, but to showcase a working Open Assembly in a different region. Given Cynosure's focus on RP, and the lack of focus on gameplay, the Senate offers a very relaxed atmosphere. It's only really used when needed, and even then it works on consensus, so that the outcome nearly always has the support of the region behind it. If done right, an Open Assembly can offer a far more cohesive outlook towards legislating.