From what I understand, you use your Google account on Android TV. How does this work with apps like Gmail, YiuTube or pretty much anything else that contains personal and personalized content? In case of Gmail, would anyone who's using the box be able to access my email? Screw with my YouTube playlists/recommendations?
There is no 'Gmail' app in Android TV. So, no one is seeing your personal emails.
I created a "family" account which the Android TV's use we also all load on our phones and we use for google voice. This way our "shared" content is available to each person in the family and our personal stuff stays private.
An Android TV 7.0 (Nougat) allows for apps to utilize multiple Google profiles. There may be others but Google's YouTube app is the only app I've found that has this ability so far. It does work great on my Nexus Player. My daughter can watch her stuff without polluting my YouTube subscriptions / recommendations with her videos about Legos, princesses, whatever. When I'm ready to watch YouTube, I can switch it back and all my subscriptions and recommendations are there. The Shield will be getting 7.0 shortly and hopefully the Mi Box. Once there are more 7.0 boxes out there I'm hoping more apps will come with the ability to switch profiles.
There is no Gmail app on the TV and by default no web browser so no one would have access to your email unless you installed a web browser and logged it in to your Google account.
People will have access to your YouTube account and could subscribe to different channels, watch ones you are subbed to, and thumbs up content but that is about it.