Does Brynhir Thundersong prevent opponents from playing cards only on the turn it's played, and does it affect cards already played before Brynhir resolves?

Ruling: Opponents cannot play cards on whatever turn Brynhir is played. Brynhir has no effect on cards that were played before it.

Sequence:

• Brynhir must be played and its triggered ability must resolve
• Once resolved, opponents cannot play any additional cards for the remainder of that turn
• Cards already played before Brynhir resolves are unaffected

Nuances:

• Players can react to Brynhir's triggered ability with reaction spells before it resolves
• In FFA (multiplayer), all other players are opponents and will be prevented from playing cards once Brynhir's triggered effect resolves
• Recycling and discarding are not being killed and do not trigger Deathknell effects
• Promising Future interactions with Brynhir are unclear and have conflicting official responses