I like that time-based mechanism much better. The karma/engagement-based stuff would just let popular people post more :)
Example. A -I released this tool!
B - Wow nice how long did that take
A - Thanks, 6 months.
At this point, the conversation is done unless both like each other's comment, which in such an exchange would be encouraged.
If C comes along and says 'this tool sucks', even if 50 people like it, if A doesn't, C is done commenting for the day.
In fairness, I haven't really thought the whole thing out in detail, just some rough ideas. I appreciate pointing out challenges and dislikes with it though.
Though if anyone wanted to set up an information farm, by creating a bunch of accounts, where they post and like each other, acting like different individuals, it could still create engagement with other innocent people who could eventually become biased, hateful and misinformed.
B might have just logged off, or maybe their question was bait to intentionally silence A. Either way, A is probably annoyed with B.
So going to a subgroup of your likeminded people would do nothing. You can comment 'like me pls', which would take you from one credit to 0. The responder liking it would take credit back to 1, which is where it was initially. So, nothing gained.
However, one would have to solve the multiple account problem, which every site has to deal with.
So if you want to write mean things, do so in your own posts without bothering others' discussions.