Because I did not get any answer if the suggestion I made is OK.
Well, I had initially proposed the settings, and you added a GUI suggestion, so you could take it that I was not opposed to it.
But having said lots I left it it to see what others thought, there are other contributors to Geany.
But, in the current world situation its not known how these various contributors to Geany are going, many have not been heard from for some time, and some countries are doing it tough, so I would expect that volunteer contributions to free software projects are not the top of their priority list. Maybe a picture and some words are possibly not motivating enough to comment if its never been a problem for them.
That doesn't help you much I agree, but its the state of the world.
But even in a perfect world you would never get a guarantee of acceptance before the PR, at most a "might" be accepted.
Still, having an actual pull request may be more enticing to others to comment, and would provide more information on how it would work.
Re-implementing the compile/build system in a plugin is a fair amount of work, just to get next/previous error to skip some lines. But as I said, its your choice whats most important to you.