The suggestion isn't a bad one but don't we have specific board for that purpose already? If you're starting a thread and you want only the opinion of higher rank users I guess that most be a serious discussion and it can be posted on the Ivory Tower board for full member above to air their views.
And we should bear in mind that those boards by design only allow really relevant topics of discussion. If one is found to be repeatedly spamming there, they stand the risk of being restricted or banned.
Making an option to restrict lower ranks on any board is a function that could easily be abused.
One of the disadvantages of self-moderated threads is the risk of accusations of political bias...
...One alternative option could be the ability of a thread starter to restrict replies to certain ranks.
There could be accusation of political bias in both scenarios.