Since many people keep asking this, I’ve put together a standard response to help clarify the issue:
In the original prerelease notes there was a statement that regrettably was lost when it was updated to the final release notes. This quote was:
"In PvE events (outside of the new Coalition Challenge that runs on the weekends), you can create decks using any cards in your collection. We are now running PvE events all week long - we are starting with retooled versions of Revolt against the Consulate and Fateful Showdown. Every Monday to Thursday, one of the two events will be available to play. The events have been reworked so they no longer are Coalition Challenges but instead are in a similar vein to the Oath of the Gatewatch event."
The final release notes now say:
“Trial of Zeal, a new PvE Coalition Challenge where you face off against the Gods of Amonkhet. Similar to previous Coalition Challenges, your Coalition will work together to defeat the Gods of Amonkhet by winning encounters and completing objectives.”
Brigby also confirmed here:
https://forums.d3go.com/discussion/comment/684319/#Comment_684319
“That's correct. The coalition challenge, Trial of Zeal, is intended to have the card set restriction applied to it. All other PvE events should not have any restrictions to deck creation.”