Yep, think Andras floated that idea as well.
We asked much earlier in the year if 4 courses of 75 would be acceptable, and the response from the chair at the time was that he supported our efforts to make the worlds competition as good as possible.
Either way there are solutions for 3-4 days, which accept 3-450+ depending on if capacity or room are limited.
As you say, the plinking range for a comp with 450 would be massive (1.5m per person, that's one hell of a line).
In any event, what will be massive is the amount of non shooting volunteers we will need to run the event. Line marshals, relief marshals, stats etc... it's going to be a mammoth task to put on the largest single discipline shooting event the world has ever seen, but with the right support, we could have a mega event. The red arrows have just gone over here, i'll stop them at the airport on the way home and see if they're free for a flypast around 2020...