You could certainly imagine somebody developing a proxy server that runs on your computer that sucks out content from your TiVo, converts it to h264, and streams it to a Chromecast. (Maybe this would include an on-screen UI, or maybe it would use your phone. I don't know.)

The TiVo UI, itself, is built in Flash, and given the glacial pace of software development at TiVo, will not be rewritten any time soon to run in HTML5.