Like searching based on filename when metadata isn't available, or showing long filenames in search results. These are considered to be stupid last time I bothered checking and I've since given up. It's a bizarre culture.
Either way, you could either:
a. Take the time to organize your library, like anyone who successfully uses Plex has.
or
b. Provide metadata to the open databases that Plex uses, to help both yourself and the next person who needs it.
The important thing to remember is that Plex is not made by wizards... it's software, and for it to catalog your library you need to name your files in a way that it can comprehend.
The notion of being able to find and play a file that isn't a formal mainstream movie doesn't seem all that obscure to me, and doing a search on filename isn't exactly what I'd classify as wizardry or difficult to implement. At the very least it doesn't seem like a crazy idea.