Earlier quoted context omitted.
This proposal would give a relative penalty to people like me who get into lengthy discussions, and who reply in older threads. Whether or not this is a good thing is a matter of preference. (My preference should be obvious.) Though, truth be told, I've never worried much about karma.
This is true, but it is a problem that currently exists. For orthogonality's sake, I would suggest that if most of your posts come from 1:1 conversations, post by post, then perhaps there is a better medium to communicate with that person than through a board like HN.
As an example I give you this discussion. In this thread I have 2 posts, both with 1 karma right now. I do not expect them to go up much if at all. Where would you suggest that I should have gone for this conversation with you?