Star nosed moles, and biblical kinds

Most mutations are neutral! The arc-organisms had a lot of additional information on their genomes. There were different paths to lose information, without dying directly. It goes on until the genetic material becomes irreducable; a left-hand wall. Yes, it depends of the type of genome of a particular specie. That's why the scenario isn't that inappropriate. Degeneration can not go on infinitely / in eternity, the species are now more or less in equilibrium. So, you don't have to assume that there will appear 2 new kinds of elephants in the next 50 years.

Nobody studied it. The hypothesis itself is dismissed beforehand.

It's not untestable. Hypotheses are often formulated to match within a larger framework by the way. I shall mention a few options to test:
Option 1. Try to generate a common ancestor with extrapolating the occurence of mutations towards the past. If there exist many genes in species without remains in species with the same ancestor, then degeneration is falsified. (Many new genes in evolution terms)
Option 2. There was one man on the arc, and several woman. The 'mitochondrial Eve' would be older than the 'X-chromosome Adam'.
Option 3. Try to develop a theory in which molecular and fossil clocks are ticking at the same rate. You've choosen option 3 if I'm reading well. So, you should add this evidence.Else, I don't know what you're saying:

• The genomes are different
• The differences are caused by mutations
• The genomic mutations distances are inexplainable by degeneration?

Or are you saying that there is a hierarchy, evolution followed by further evolution? But degeneration can be followed by further degeneration, too. Random mutation is involved, it accounts for degeneration.If I had to defend evolutionism, I would choose option 1 to attack, by the way.