I think wikimedia-l would work fine and make sense. We probably don't need an additional list, a lot of the lists we have now are lightly used.
I appreciate that Erik unsubscribed from internal-l. I think more people should do the same thing, on the principle that discussions about the Wikimedia Foundation and projects should occur in public. Herding debate into an exclusive clique is antithetical to the ethic of the Wikimedia movement.
If the lists have a different tenor such that some people prefer internal-l over foundation-l, then the solution is more active moderation of this list. Foundation-l moderation has been absentee for sometime - I don't even recall the last time a list moderator participated in a discussion, let alone took a moderator action.