I think the concept is great, but the motivation for the privilege levels is somewhat flawed.
It should perhaps be considered on a case-by-case basis, but the privilege threshold is one of the key reasons why, for example, I wanted Code Review to graduate.
Escalated privilege thresholds is a good thing for a site - it encourages people to be more thoughtful about their contributions, it gives additional goals to strive for, it is a motivator.
In addition, it keeps people new to the site out of situations which can cause them troubles.
The reasons beta sites have lower thresholds is because nobody has high rep. If the site is stable enough to be called "mature", if the site is competent and capable finding and electing moderators, then they are equally capable of having trusted users, etc.
The delay for the implementation of the threshold is likely to cause as much damage for some sites, as good for others. At a minimum it should be considered on a site's merits.
Apart from that, I think this is a great stride forward for Stack Exchange
