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 if you're looking for lower rank replies (minus newbies) then the serious discussion will give you replies from jnr members above.

Again let's not forget those boards with rank restrictions aren't that active and the same thing might occur to the self moderated topics with rank restrictions

Also I see a big disadvantage to this because it might get abuse, higher rank users might start creating threads just for themselves and this will deprived the lower rank users with quality at hand to contribute/interact with the higher rank users and possibly get reward with merit to rank up.