The VB one says: "The administrators would like you to read a thread, please click here" if they dont view it then they just see the message.Not quite as thorough as Forcing someone to read a thread, which I thing has a usefulness unto it's own.
This idea would trigger an alert to everyone - the message could be to tell them to "Read thread X now".
Maybe do another read the thread now warning.
After that, where they've had sufficient warning and chances ... maybe this force users idea would be appropriate.
But maybe an alert to everyone is a better idea to start:
It would be interesting if someone creates an addon as linked in the first message. There Borbole addon but can only be used for a thread.