I know, I'm already doing that too and it works, but not all of my video files play correctly.
If LG wants it it's possible probably with just a software update. Besides being compatible with the most popular video player in the world is also in LG's interest.
Because if this is possible it's yet another reason not to buy a Chromecast and people will continue to use Apps from within WebOS, and not Google TV, which obviously is a competitor to WebOS. So really it's just a matter of letting higher-ups within LG know that this is a feature people are still buying Chromecasts for.