cracksloth has made a good case for this feature in previous thread, and for the implementation of plugins and stuff, but i'm afraid that it may just be too much of trying to add a totally independent application to f&r. in other words, why would it be better to use f&r to do this compared to using a real (but small windowed) file explorer? ie if it uses none of the features of f&r, then it probably doesn't belong in f&r. there is so much to do with f&r that i think we should focus on a search tool rather than a generic "small window popup tool" which can host any plugins. [we can talk about such a project as a separate tool later, perhaps as a generic docking bar thing]
having said that, there were ideas that cracksloth raised about adding file browsing or file previewing capabilities that i am still tempted by. for example, it might be useful to be able to search for folders, and then double click to launch them in a (customizable) file browser. so for example if you typed "mymp3s\" then it might find all the DIRECTORIES with the string mymp3 in them (maybe scoring those ending in mymp3 highest, since its probably what you were looking for), and then you could double click to launch and browse that directory in your normal file explorer.
or if we really wanted to get fancy we could try implementing one of those kinds of file "preview" panels so that when you clicked on a file or folder an optional panel would show you a preview of the file contents (depending on the file type), or folder contents. but then i think this might be more work than its worth, and we might be better off letting a standalone preview/explorer tool do the job.
i'm also still struggling with the extent to which f&r should move to be a more effective document (as opposed to program) searcher. ie allow people to more easily specify dynamic folders to search in for each search; ability to search within files; ability to search things like mp3 tags, etc.