I think your idea about the top Host stepping down periodically is a good way to divide the hosting duties. The way I envisioning it working would be for there to be six hosts. Every month or two the top host steps down and every one else would move up one spot. The initial order of hosts would alternate between 'free-thinkers' and 'skeptics' and would then be maintained by that simple rotation. To fill the empty number six slot, the new second slot host would assign them - so a 'free-thinker' would be nominating a 'free-thinker' and a 'skeptic', a 'skeptic'. The second host could choose the number six host however they wanted, but it wouldn't be a bad idea for them to start a thread for group members to volunteer or offer nominations. (Or people could PM them since they would know who would be deciding well in advance.) I think the other hosts should probably have veto power over the final selection - but only by a unanimous vote against.
I'm not sure if that is roughly what you had in mind or not; I just wanted to spell out my thoughts on it in more detail.
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I still don't see that a nomination/tally couldn't be workable and would necessarily turn into an all consuming discussion. Every three or six months we could simply pin a thread for a week or two where people could nominate an even number of persons for hosts - half 'free-thinkers' and half 'skeptics'. No other discussion should be in the thread except that: nominations. Then when time is up, the current hosts tally up the results and assign the new slots accordingly. The idea of an alternating top spot could also be implemented (although that may not even be required as I would hope anyone that garnered enough votes to be in the top slot would probably be seen as fair to most people anyway).
As it stands, the nomination/tally plan is probably the only way to go about picking the initial hosts anyway. I guess we'll see how difficult the process is and whether we should voluntarily subject ourselves to it repeatedly. Obviously there are more details to work out and be agreed upon, but unless someone else comes up with a different approach I think your two initial ideas are the basic framework we should be proceeding with.
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One other thing to discuss would be removal of hosts before their "term" is up. Would we leave this up to the Admin? A super-majority of the current hosts? A referendum of the group members?
I'd be satisfied with a super-majority vote of the 5 other hosts for removal. I don't want it to turn into a call for removal over every single controversial decision by other group members, but rather more for a series of decisions that people can make a strong case regarding their actions. It's likely that many people will have differing opinions on this, but I'm not opposed to keeping it simple.
Once a host is removed (or just needs to retire for any reason) the process to choose another would be different depending on whether we end up using the top host stepping down method or a simple nomination scenario. For the latter it would be easy: all hosts move up and a nomination/tally thread decides on a new host. The top host stepping down method would be a little more complicated. The remaining hosts would move up as required to maintain the current 'free-thinkers' and 'skeptics' alternating positions, which would open up either slot five or six. If slot five is open, the top host would choose the replacement; if the opening is slot six then the second slot host would decide.
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Once we decide on how to select hosts, we also need to agree to how they will go about actually being hosts. Do we want special guidelines for this group? Or should they just have the normal group host abilities that are designed into the DU3 system?
I had hoped that some other people would stop by to share their thoughts and ideas on this matter. Perhaps they're still over at DU2.