I think that you have a very large problem without realizing it. This diagram helps illustrate this:
The problem is just that while the idea might sound nice, that there is some boundary past beyond which further transitions cannot occur, there is no line that anyone can communicate. There is no agreement amongst those who reject common descent what is related to what and what doesn’t share common descent. There is no, ‘variation within a ‘kind’ shall stop here and no further.’ The problem being that the second anyone starts to go and identify what belongs to a ‘kind,’ the original ancestor of kinds start to become ridiculously similar, more similar than the species within each kind as this article highlights: