I recently received an email from Microsoft promoting the upcoming Titanfall and console deal and at the footer of the email there was some useful information regarding the installation size. Everything else was pretty obvious.

Titanfall is a fully online experience. To play on Xbox One or Xbox 360, you'll need to purchase an Xbox Live Gold subscription. Titanfall bundle: Titanfall game download card inside marked packages; up to 40GB required.

So there you have it, we now know that the digital download version of the game will require around 40GB if storage space. Minus any future updates or dlc.

I was expecting this so I'm not surprised but it does raise the question as to when Microsoft will allow external HDD. Anyone looking to own 10ish or more installed games will soon be running out of space so I think it's an issue they need to fix as soon as possible.