Dear Lady, don't get the idea this concept is saying a large scale saltational event is occurring, it is more like a slow 'partially or totally hidden' bit of evolution occurring before its relatively sudden expression.
If this mechanism, or process if you prefer, is the active process in a population... oh, evolving legs let's say, the legs would not end up being full blown legs like yours or mine, but simply a larger scale 'change' to existing features, such as fins, than we would normally expect, or it could result in 'leg buds' where an existing skeletal feature is replicated in another place or modified in place - such as an additional segment of bone is added. For true legs to result from these 'buds' it would still take hundreds of generations. Remember what geological time really means.
Would all of the particular species acquire legs? What if a particular species were separated by great distances? If they were in close proximity to one another, would genetic drift affect all of them at the same time?