During the latest Active Time Report Broadcast, Final Fantasy XV Director Hajime Tabata mentioned that Share Play will be blocked in the PS4 version of the Episode Duscae demo of the game.

On the other way it'll be possible to broadcast and upload video normally.

The reason given for the decision is that Final Fantasy XV: Episode Duscae is simply a demo, and not the final product. If you want to play the demo, looks like you'll have to grab your own copy.