User blog comment:Master Sima Yi/Assassinews 19-03-'14 – Two Assassin's Creeds for 2014?: Unity and Comet/@comment-3046679-20140610114708/@comment-27202257-20140610145253

On two points, it looks like the HUD added to the screen can be actively toggled on and off, and least that's how I interpreted it. In that case, it would be a damn godsend we didn't even know we wanted.

As for the co-op, I'm not sure what was up with adding those three in at the last minute, but from what I've gathered co-op will have its own narrative-based missions. So while some missions are strictly Arno, you'll still get useful story info out of playing cooperatively, and Ubisoft actually expects you to spend about 1/3 of your playtime doing it.