For now unused sMerit decaying still not implemented.
There are lots of users who are actively sent their sMerits away to deserved threads. I agree that someone who didn't send their sMerits. There are several assumptions why this happened.
1) Those users have not logged in their accounts for a long time before or since the lauch of merit system ----> They might send in the future.
2) Those users have actively used their accounts in the forum, but doesn't familiar with merit system. Maybe they don't care about this or a little bit busy to spend their precious time to read information about merit system's mechanism. -----. They might too.
3) Those one who never care about merit system and their sMerits. ----> Mostly wont' pay attention to their sMerits (for those cases, demeriting is needed), but I guess number of that sort of users are very low.
More importantly, Merit system has experienced around 2 months (since January of 2018); so we should wait one or two more months to see what it will become and how sMerits distributed in the forum.
At the moment, I think merit system has done its good original objectives (controling spammers; discovering merit farmers, etc.)