Interesting idea and I would really like to see such a proposal at least some time as a trial.

While "ignore" is indeed a very hard punishment, especially when it comes from a Merit source, a "hush" could be like a second chance.
At least for semi-constructive accounts.
However, I don't know if participaction is high enough to result in a resonable added value for a "hush score". A hush score, where almost noboby is participating would be pretty meaningless.
I'm sure we could find incentives to use it but then, we should also consider the following thing:
Display posts from accounts on our "hush list" changed to (dark) grey.
Doing so, would make posts still visible but you can skip them more easily:
I'm hush and I'm here to shitpost, therefore, I#m on the hush list of many contributors because my posts are so generic...
That way, I can "hush" with reckless abandon and still be assured that nobody will fall off my radar forever.

Considering the fact that users could get abandoned on a radar forever,
At least plagiarizers should be hushed for some time (until their next plagiarism is reported)