This trust means that they can access to admin's account. Thus they have full powers just as theymos does.
Even if we assume that such a trust exists, the large number of admins will cause some bugs + any hacks of these accounts would threaten the forum as a whole.
Also, the process of restoring accounts is not merely a sign/verify the message.

The best solution is that theymos trusts the investigations of some members and thus recovers those accounts based on their recommendations.