Users should get a trophy for 200 forum post.

I think it would be cool man. Plus give more people a reason to post. This has nothing to do at all with this being my 200th post btw :)

But it would give an incentive for trolls and posts for posts' sake.

Yes, #2 is right.

Nah, I don't think so; no-one has more posts than I, in the entire site, BTW. :-P

#2 LOL A spam abuse trophy it will be called

I've posted almost 1/4 as many as @Neverness! I should get a trophy for that.

Yes, it would just encourage people to post whatever for the sake of posting, just to get the trophy. Maybe a better trophy would be for playing a few thousand rated games, or winning that many, or getting a certain amount of tournament points, to encourage people to play frequently and well and reward them for it.

Not any forum post, ... but more like proposed features that got accepted. Not a trophy, ... but more of a thank you for the ideas.
Over time, ... people could start brain storming new and better ideas and the coders could get a coder icon in their profile.

But coders do get an icon in their profiles. Look: en.lichess.org/@/Clarkey

The forum is already a mess, with many posts like: check out my excellent game from a 1300 rated guy with many blunders. Or how should I win stockfish 1. Or how should I improve my 1200 rating or become a grandmaster in 6 hours.

Why do you want this place to be worse?