Making it expensive to create identities directly undermines the goal of having mining not controlled by particular parties. Moreover, any such scheme has some optimal strategy where the cost of identities vs exclusion are counter balanced, and in general complicated strategy favors larger parties (who can afford to figure out and implement the strategy). Also even if you had a perfect identity scheme (which could trivially be used to impose external control by ordering the identity holders to do things, but we'll ignore that) it wouldn't work because parties could permit others to use their identity.  (E.g. to mine at this pool you must obtain an identity and allow the pool to use it).

In any case, it's hard to comment with more than these sorts of arm-waving generalities against a proposal which is itself an arm-waving generality.

Please take the time to concretely work out how to intend to issue and manage these identities, and what effect(s) you have them to have before asking other people to spend time considering your idea. Otherwise any reviewers time investment is unboudned as you can continually reveal previously undisclosed features which patch over their concerns one by one.