The binman chronicles
Player Valuation: £80m
As ever, the crush or slowing only occurs at the actual pinch points, not in the open space, however big they are (a bit like closing lanes on a motorway, congestion soon ensues if flows aren't maintained). In this case a few relatively narrow openings in the dock wall. Their size will dictate how quickly the site can empty. First impressions suggest that that will be akin to emptying a full Goodison plus another 14,000 fans via say Gwladys street and City road only. With the added complication of having to channel 3-8k away fans through the same routes.
Keeping a proportion of fans behind longer is desirable for several reasons such as: further income streams and to relieving pressure on public transport and road networks etc. I can remember suggesting it to the stadium manager years ago.... he said they had trialled it at some point but the response wasn't great and that even the lounges emptied quite quickly after night games. So the onus is on designing for safe and effective eggress for the worst case scenario of (for instance) a night cup game.
Some grounds are notorious for people leaving early..... this is often because of the issue of poor egress/public transport. So it is another major issue to consider.
You are right that there will be a pinch point at the dock wall, but I don't think I will be as bad as you think. At Goodison you have narrow concourses/exits leading out to minor roads. The congestion there will be worse than anything at BM despite only being able to exit via one main route. The east stand and south east corner will have a pretty straight run out and the majority of that stand (the ones that don't want to stay that is) will have already left the fan plaza and be out on the super wide Regent Rd by the time the bulk of the west stand occupants start to hit the FP.
With the large area under the outdoor steps on the west stand and plenty of space in the plaza to stand aside and let the rush go by will also aid that process.