It could be a useful discussion, but only if you can come up with a way where miners/pools can not easily create new identities without relying on a central authority.

Like gmaxwell said, if it is economical for a large pool to create new identities to work around any form of block-finding-speed-restriction (such as the proposed exponential backoff), they will do this.

Falling back on a central authority, such as the Bitcoin Foundation, like you suggested is not acceptable. The Bitcoin Foundation is not in control of Bitcoin and plenty of people don't even like the Foundation (plus it's a purely American group). But any central authority being able to control who can mine a block is a polar opposite to the design goals of Bitcoin.

While centralization in some cases, such as exchanges, is hard to avoid, in those cases it typically involves optional services. Mining is at the foundation of Bitcoin. If that is controlled by a single authority, Bitcoin loses its purpose.