The idea is interesting. This would encourage people to write quality posts and possibly further reduce the amount of spam in this forum. But on the other hand, capitalize merit quite difficult and it can result in a new wave of sales merit and will give the opportunity to influential accounts to capitalize on this. Merit as gratitude for useful information will almost never be applied.
To partly avoid the situation bounty reward could be paid not for the count of merit points but for how many
different users merited the message.
For example
1 user merited the message - 1 stake
2 users merited the message - 3 stakes
3 users merited the message - 8 stakes
5 users merited the message - 25 stakes
So it's not matter how many merit points you get from a single users