Coventry should have ticket barriers again. Sandwell and Dudley and Wigan North Western should also have ticket barriers. Birmingham International should DEFINITELY have ticket barriers - the design of the station makes this ideal. (
http://www.nationalrail.co.uk/stations/sjp/BHI/plan.html) It could be a similar design to Waterloo!
I'm not so sure about Wolverhampton. I don't know where they would go without causing inconvenience to passengers. The same applies at Lancaster (it has multiple entrances), Preston (it would be horrible if ticket barriers were installed here!) and Warrington Banq Quay.
Although I agree that ticket barriers
should be installed at all of these stations, a balance must be struck. Ticket barriers are OK when they "blend in" (like at Waterloo) but not when they cause inconvenience to passengers (like at King's Cross, though I appreciate that the crowding problem will be "cured" somewhat once the refurbishment is complete).