I would say that if using it in writing it would have to be in a fairly informal context, e.g. dialogue between two characters, or in a short informal conversation, however in these instances I would either drop the 'are' or contract the 'you are' to 'you're'
e.g.
You're going to the stadium tomorrow?
Sounds perfectly natural to me
NB. Just had a thought, this would only really make sense if the topic had previously been mentioned, e.g. if you were bringing up the subject of your friend/colleague going to the stadium, then this would sound odd.
However, if asking for emphasis, or in exclamation, this would work.
Examples:
You doing anything nice over the weekend?
Yeah, thinking of playing a bit of football with some mates, want to come?
*You're going* to the park?
But:
You doing anything nice over the weekend?
Not sure yet
*Are you going to go* to the park?
Arefrequently. – Tushar Raj Jun 11 '15 at 12:45You are going to the stadium?puts emphasis onstadium, and can be used when this emphasis is desired. – Tushar Raj Jun 11 '15 at 13:00