I've been looking into this today and it seems some parts of Windows will play the file while others won't.
It looks like the API used for the basic Play window in Opus will not play it, at least without adding an extra component, so we'd probably have to re-write that to use another API for it to work with the file.
However, if you just need a quick way to listen to these files while in a folder, you can use the viewer pane and it's potentially better than using the Play window as it is easier to switch between files.
To do this, you'll need to disable the WAV plugin under Preferences / Viewer / Plugins. (The WAV plugin just displays thumbnails of WAV files; it doesn't play them.) After doing that you should find that WAV files play in the viewer pane using an embedded instance of Windows Media Player, which will handle the format.
That's ideal if you want the files to auto-play as soon as they are selected, if the viewer pane is open. If you would prefer to have to click "play" in the viewer pane instead of them playing automatically, go back to the same Preferences page and configure the ActiveX + Preview + Office + Web plugin, then enable Preview Handlers / Windows Media Player at the top. That will make it use WMP via a different route, which is click-to-play.