There are Foundation-level issues that need to be kept to some degree of confidence. Although, frankly, I think "all admins" is too broad of a level to release most of those items because, quite frankly, we have a great many untrustworthy admins.
Trustworthy or not there are hundreds of active admins. Anything discussed in an Internet forum with hundreds of people is very close to being public information.
Most of the regulars on wikien-l are old hands anyhow. I'm not sure if you'd get a substantially different forum by creating an admin-only list.
In any case it would mean a substantial change in what it means to be an administrator. This should be well advertised and discussed before it happens.
Regards, Haukur