The question doesn't really relate only to Project Protected Profiles, but actually relates to all profiles, and that is the question of how to handle research in progress.
Magnus is of course right, that the end-objective should be a bio that is clean and contains just the end result. But where there has been controversy or discovery, the end result should include sourced information related to the resolution of the controversy or discovery. You can write a brief bio for John F. Kennedy because his genealogical and biographical facts are essentially common knowledge and there is no controversy about them. Even so, the facts that are cited in the biographical narrative must be sourced, because the sources in the narrative are the only way one knows that the dates and relationships in the data field are not fiction.
Where there is controversy, which has been resolved through research and discovery, however, the should be reflected in the narrative, or else people will not know that the controversy has been resolved, and tend to recreate it.
I would think that the decision to go to a supplemental free space page would be determined by the amount of material involved in the controversy and the complexity of the response. I created a free space profile in the case of Katherine Marsham -- http://www.wikitree.com/wiki/Space:The_Legend_of_Katherine_Brent_Marsham
-- because the discussion needed to be fuller than would fit on one profile, and affected a number of profiles. In this case, however, my motivation was the opposite of that suggested in the query -- my desire was not to have a forum where more people could participate -- G2G is best designed for that -- but where I could present an analysis that I claimed ownership of and restricted editing to only 3 of us on the trusted list. That then facilitated covering only the essential points on affected profiles, with a link to the free space page -- which, as noted, had the advantage that it could be a resource for several profiles, not just one.
In general, one of the strong points of WikiTree is that it accomdates the differing research and writing styles of a number of people. Anytime we standardize an approach, we are forcing someone to adapt their own style. Some standardization, of course is needed, and teamwork means making some adjustments. But we should standardize only when there is a strong necessity to do so. We capture more of the energy of diverse volunteers when we maximize the freedom of approach. Suggesting that free space profiles can be helpful in certain situations is a good thing to do. But suggesting that everyone should use a free-space profile in all instances of a certain kind is unnecessary standardization which will simply suck out the energy of otherwise enthusiastic volunteers and unnecessarily cost WikiTree the enthusiasm which has taken it so far already.