This would be ultimately filled with trolls, nonexperts, and people with an ulterior motive or grudge: so any such effort would be less trustworthy than the original publication.
If you want to find mistakes, you can find one in every paper. The character of the mistakes is important - is it fraud, is it incompetence, does it negate the results? Or is it good science being done by a human? An open website doesn't seem to me likely to be able to draw that out.