The Comprehensive Rules update resolves the Equip-Fail issue. In order to announce the rulebook Equip in good faith you now have to have a legal card to play, and pay Gold such that you can actually play it. Note, however, that Temple of Serenity's action still can be used without a Spell in hand.
Thanks for this patience on this matter, we wanted to have a solution that would work, would fix some other problem rulings and would be somewhat compatible with the 20F rules in which Equip targets its attachment (so that,come 20F,only the clause about the rulebook actions needs to be removed from Good Faith).