Core
I think this, or a dedicated forum, will be the right place to discuss things, ideas, proposals, links, etc about the future Tiki architecture, and things related like external modules, how will be the core and what will be there, and post agreements/ideas/etc on topics discussed here in Wiki pages related to this topic.
The comment system for wiki pages look a bit weak on what and how could be expressed there, and the other alternatives for this discussion could be a dedicated blog (but is more to show how things evolves, like a diary on what we are having clear that will be in core) or the dev mailing list (but this thread will be lost in there). For now a thread in this forum seems to be the right way to start the discussion, and put what is concluded here in wiki pages and blogs (yes, TikiIntegration2 gives a hint how all of this could be integrated, but lets use what we have now)