A scene would freeze, and you couldn't tell: is the person thinking, gone for good, or simply hasn't noticed? Meanwhile NPCs stood around waiting for someone to walk up to them.
Waiting for your post — a marker with a deadline right in the scene: you can see whose turn is holding things up, and for how long
Waiting gets acknowledged — you can flag that you've seen it and will be back, so the scene stops hanging in silence
NPCs make the first move — an inhabitant can pull a role into a scene: call out, catch up, refuse to let go
Archive of application rulings — the GM sees who was refused or approved and why, and can revisit the decision
You can still keep people waiting. It's just visible now who exactly is waiting.