I own a Chromecast and like all about it except it's ability to play oyur own content. I understand why they forbid it, but for the same reasons I'm using it much mroe rarely than I would otherwise. Additionally this could have easily been an addition to the original Chromecast via a simple extractor.
I won't even run the Facebook or LinkedIn apps without locking them down first. Frankly, it's somewhat negligent that this isn't built into the Play Store installation UI.