Most projects have an issue tracker where one proposes changes or reports bugs. The IRC channel is labeled "Support channel for darktable" rather than "Tell the developer how they ought to better serve me for free"
People have a finite slice of their life to give you for nothing. Putting specific suggestions on the issue tracker seems more respectful of their time.
I raised a ticket on an open source project about a defect. It was open for 6 months with no comment. So I fixed it and did a PR. The PR was still sitting there open after 6 months. More interesting PRs to the developers have been merged.
What I usually do when I see promising projects and slow devs.
1. "This one issue is what is stopping me from using this product. Is this current method preferred by your users or do you have any other reason to not want to change?"
2. "The proprietary solution costs $X per month. Is there any way to sponsor development? I am willing to give $X/n (where n is whatever number you are comfortable with) per month to get this issue merged and to have some sort of prioritization when triaging issues.
3. Failing those: write a blog post and propose a fork. This is usually the quickest way to get a reaction from narcissistic developers.
It's the busiest developers who would be interested in receiving PRs. If they go unanswered for six months, it is a clear signal that there is something stopping else them from action.
It is also an opportunity for someone to feel involved and eventually join the group, perhaps even become a maintainer.
Speaking as a project maintainer that is starting to see some traction: I'd love to see people coming with PRs for features. It would mean a big amount of validation.
People have a finite slice of their life to give you for nothing. Putting specific suggestions on the issue tracker seems more respectful of their time.