Hoi,
At the WMF language committee, the question if a language is viable for a Wikimedia project is a practical one. It is also very much a political one. One vitally important difference with your approach is that the distinction is between a first project and a subsequent project. In the latest iteration of the approach we do not consider Wikidata a first project. Relevance is that we do not require localisation of MediaWiki or an Incubator stage.
When the question is what it takes for a new project to work? .. the simple answer is "a few good men". There are a few projects that are alive and well that rely on no more than 3 people.
By not focussing on Wikipedia, it is possible that a Wikisource becomes the first project. When this is what those "few good men" want.. It is their party.
You may imagine that we thought about what are the likely success factors for a new project. We did come up with similar ideas that you have. The problem is that it does not help. So you determine the likelihood of success, it does not guarantee it.
What we certainly do not consider is the number of data sources. Sourcing is very much a luxury in starting projects. Insisting on sourcing at all will kill most initiatives immediately. What is important is that people start writing, reading in their language.. With a Wikipedia that gets active participation / readership, there will be a move to a more consistent orthography. Those that write determine in the end.
Wikidata was given its exception because it represents the lowest level of participation with the most effect. Add one label to an item that is used a lot (human, male, female eg) and it can be used thousands of times. It is also very obvious to re-use dictionary information to make an impact.
Thanks,
GerardM