I think the better solution is to study the merit distribution for each board?  If the merit distribution is almost equal in each board (we know the drill, Meta board is one of the highest merit distribution hence it really attracts people who want to rank up) then there is no need to be biased in one board over the other.  I said it before, I think there is a need to study the effect of merit system to the "migration of spammers" (going from one board to the more famous board where they can earn merit).