I think the main problem with this working “in the real world” is that the system relies on artificial scarcity for it to work. If the meeting manager decides that this meeting is “really important”, s/he will plough right through any self-imposed barriers.

Instead of long giant meetings where the agenda is several high level bullet points, why not apply the GTD concept to the meeting itself. Have a very short meeting to discuss one topic that can be covered in about 10 minutes, then go back to your workspace and follow-up based on the outcome of that meetlet.

Of course, then you run into the problem of context switching. Humans aren’t good at context switching. If you’re in “the zone”, you suffer huge mental penalties for stepping out of that, and doing something else.