I definitely don't want to give the impression that I am opposed to credentials in all instances. Actually, Medicine isn't that great an example, because you don't become licensed as a physician or surgeon until you've completed a residency - ie., you've proved you can "do it". Whereas in Law, you only need to obtain a degree and pass an exam. So in a way, you really are relying on reputation in law - which may be why "big firms" like to broadcast their connections with Ivies and so forth.
Anyway, the licensing process for MDs is so different from JDs that I shouldn't have mentioned them in the same sentence.
Here's my worry, though. If a truly bright person can learn much more quickly than the average, that person may eventually be discouraged from pursuing law (or even medicine) because they are essentially throttled by the system. Also, credentials may not matter as much to this person, because they seek out areas where they can prove themselves without worrying about the particular degree.
If this happens (and I'll admit it is unlikely in the near term), you could have a situation where professions that make heavy use of credentials are most appealing to those who are good at getting credentials, but not much good at anything else. For those folks, the payoff of a credential is highest. Whereas for someone who could do well with or without a credential, it's just a path with many irritating roadblocks.
The interesting thing will be to see if the professions adapt. Perhaps there are some creative ways to retain some of the valuable aspects of credentialing without forcing everyone to learn at the same pace? Perhaps a heavier focus on exams, rather than than hours or years logged in a program? Another approach might be to limit the most restrictive licensing to more specialized cases - ie, require a 3 year degree and full membership in the bar (and, I'd hope, even more than that) to try a death penalty case, but require a shorter and easier exam for more transactional work where a minor amount of money is on the line. Even in medicine, I suspect that nurses can handle many of the things that only MDs are currently allowed to do (in some states, nurse practitioners can do this - a two year MS followed by a one year apprenticeship and exam is sufficient to independently treat some cases, rather than a 4 year degree followed by a three year residency).
Hard to say if it can happen, or if it is even desirable. But I'd guess there will be pressure, and that's not necessarily a bad thing, depending on how it all goes down...