When "none of the above" wins, it usually means new elections where all old candidates are banned or some other procedure to resolve complete distrust to current politicians.
But then the original point stands. Such a system doesn't fully allow you to express legitimate feeling that you don't know. If majority expresses "I don't know", it doesn't suddenly mean "I don't trust old guard" vote. That's misinterpretation of the voting result.
Also, you can express "I don't trust old guard" in the non-mandatory voting system as well. Just vote for the new candidate. So it's actually simpler system than yours and more expressive.
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When "none of the above" wins, it usually means new elections where all old candidates are banned or some other procedure to resolve complete distrust to current politicians.
But then the original point stands. Such a system doesn't fully allow you to express legitimate feeling that you don't know. If majority expresses "I don't know", it doesn't suddenly mean "I don't trust old guard" vote. That's misinterpretation of the voting result.
Also, you can express "I don't trust old guard" in the non-mandatory voting system as well. Just vote for the new candidate. So it's actually simpler system than yours and more expressive.