Getting a separate media player would still be the best approach.
It's unlikely that a usb player built into a disc player will be as good as a standalone media player. Sure, media files will play on a BD player with mkv capabilities. But sooner or later, you're going to run into some problems.
With a narrow field of specialization, you get the advantage of quality performance. That's true not only for video players, but also for doctors, lawyers, etc. ...