Interesting thread, which probably doesn't need my contribution, but I'm bored, so here goes.
Can't see what the problem is with the existing friends and foes option. You can live your forum life almost blissfully unaware of another with its use, although the threads a foe start might remain a mystery. Then, they might get quoted - oh well. Other than that, what is the problem?
I have been on a forum where a particular individual was quite annoying to some folks, but because the user was quoted so often, he being an excellent provocateur, the ignore feature proved a bit pointless. That's rare though.
In regard to PHP code, there is a PHP tech forum which is extremely well populated by programmers who provide their knowledge and work free of charge. They are enthusiasts, like many users here. When I ran a PHP forum, I was always fiddling with design and features. It was a little obsession with me, which is one of the reasons I gave up the forum. I know how time absorbing being admin of a forum can be. It's mostly a thankless task. (So, thank you to the admin and moderators here from me while I think of it)
The PHP tech forum was the source of all my learning about php forum software. Most of the time I took what I wanted off the shelf from what was being posted in the threads to enhance my forum's features, but on the odd occasion I would post a request for some code. I was always given assistance. The cost to me was in time, not dollars, which is the same thing if you think "time is money".