I think that there are multiple ways to get true value from this venture and, by asking our opinion, you have started down this valuable track. I hope you continue to do so.
This should be the source of great content for SSC. There can be articles, editorials and even polls all along the way. If you document the whole process then you will have a wonderful case study. As well as the technical implementations there are also the technical discussions to document. For example, I for one would love to read about how security was considered, in what contexts, what options were considered and why as well as the final solution. Publicly documenting security may feel like walking around naked but details may be redacted where necessary so I would be comforted to know that passwords were salted and asynchronously encrypted but I do not need to know the encryption algorithm.
As a user I would accept disruptions to the service, particularly if we were warned about upcoming changes, as one of the points is that we are inside the process. This would have to be our accepted cost for all these benefits. I would also understand that certain site features may become temporarily duel hosted (i.e. different URLs) with one being read only during the transition process.
Also, SSC can choose to engage this community at any level for any part of this project (if it happens). Do you discuss design or implementation decisions via editorials, for example, or even offer decisions up for review? This can only work if SSC is totally in control and is open and firm with the engagement at each point i.e. the responsibility lies with SSC so it must be clear that this is not an Open Source project but an open project.
There is even some slightly off topic articles regarding web page generation to be garnered here. As well as a lot of kudos!!!
I really hope that you guys do this.
-- Stop your grinnin' and drop your linen...they're everywhere!!!