Niall - Wentworth was proposed in the early 60s I think and Michael Bonallock was very much in favour of it. The Open then was in decline up until Arnold Palmer coming over, very few Americans bothered to come over, hardly any USA winners from 1934 to 1960, just Snead in '46 who probably only played in it two or three times and certainly did not defend it, then Hogan who just played in '53, when you consider that from 1920 through to 1934 quite a lot of Americans came over, the Open was in need of a big revival. Of course we dont have that problem with it now and the success is quite a lot to do with the type of courses that the championship is played on, the main thing to factor is how easy 50,000 can get in and out each day and where the hotels and accomodation are, airports, motorways, tented villages, auxillary car parks and all the rest of the logistical stuff.
I am pretty sure it will stay within the current rotation and probably if this years Irish is a 'succesfull trial' I think Portrush will get added for 2017 or 2018. Theres no reason why it cant go south as Ireland is still part of the 'banner', but I dont know if theres a suitable course in Ireland. Porthcawl is another that the R & A would like because its Wales and West, but it does not quite work. The biggest new threat would be Trump I expect. There are not many places the Open can go other than the current courses when you add up the requirements.