So I noticed it says unused Merit can be decayed at some point in the future - What's the point of this? Is it just to keep people from stagnating their Merit and not using it?
To increase the merit circulation, although I have never seen anyones unused merits to be decayed so far.
Also, what are your thoughts on people here using their numerous alt accounts to abuse the Merit system? Granted, there's not much to "abuse", but someone who has a dozen alt accounts, say one of them gets selected as a Merit source, couldn't that have a negative impact on the system?
It's possible that people have alt account and they are abusing the merits. If such abusers get selected as DT member and they abuse by meriting their alt account, there's no way you can prevent it. However, if the posts deserve merit, I think if someone else was a merit source, they would merit the posts. So, same to same although it will be abuse if they give merit to themselves.
EDIT (wanted to add): Are you worried about people paying for Merit just to rank up?
There might be some people who are buying merit to rank up and getting accepted in signature campaign but don't forget that most campaign managers now have a look how much merit an user gets within last 120 days and of course their post quality which meam ultimately such merit buyer will get no much benefit.