Users must be forced to spend their smerits as well to reach the next rank. If he/she needs 500 merits for Hero rank, he/she also needs to spend 250 merits to achieve Hero rank.
CV, we have a system that's already propulsive and the merit system was made just the way it is to support the function. Your proposal may seem like a better option, but trust me -- forcing people to spend their Smerits will introduce a more suitable way for bounty hunters to maneuver, putting everyone in a "race", making the system porous and destroying its essence. Overall, Theymos doesn't have any plans of compelling people to spend their Smerits.
Another idea is to get back merit rewards. Like spending 2 merits, the receiver will get 1 spendable merit.
I'd love to ask again, what exactly would be the point of having the merit system in place? This proposal breaks the only limitation and creates an infinite production in the merit system. So, I don't even have to merit other users for post-worthiness, I just need to send a bunch of merits with the hopes that I'll achieve my ranks.