I think the question here should really be "What are the minimal requirements for a conceptual paper to be a worthy addition to the academic literature". Academic literature is very different to everyday literature where when you want to introduce an idea to people you write an article for a newspaper or a blog post. In academia all ideas being introduced, including conceptual ideas, need solid evidence not just it would be worth working towards. Looking for an "open-minded editor/journal" probably more likely to lead you to you finding somewhere worthless, crackpoty or predatory which you end up submitting your article, ruining your reputation and/or losing you money.
When thinking about conceptual ideas, keep in mind that ideas/questions are cheap, implementation is key. You may also have heard that the key thing for research is a good idea/question, and I also agree with that, but its a good idea/question that's worthwhile. And a good idea/question is essentially one that is easy to implement, since most ideas/questions are hard to find anything academically useful from.
So what should we have in a conceptual paper, probably the simplest thing is evidence and an understanding of how it's building on previous academic work. If you think the field should adopt a new idea or more people should start investigating this topic then you need solid arguments as to why this idea isn't stupid and starting points from which researchers could build upon. Generally I would guess back of the envelope calculations or early and incomplete data could possibly be sufficient here however they still need to be solid and robust to challenges. When talking about the new idea/question it needs to be able to link back to previous work to support it or needs to do a literature review to show that tool X from field A could probably be hacked together to be useful in field B, and the back of the envelope calculations could support this. The conceptual article should also point out how this could be a natural progression of the field and list the possible problems with the idea to try to help others see where the struggles would be or speed up with the debunking of this idea. It could also propose some solid good questions that the author thinks would be valuable to answer but doesn't have the time/skill/resources to do so. But for this to be a worthwhile piece of academic work the context is very important, a new idea with only back of the envelope calculations isn't a research article, its a project proposal at best.
Once you ask what is needed to make the research solid then being unable to find a relevant journal should either go away or become an issue of the research not being solid enough to be of interest. No need to search for "open-minded" places.