Royal Porthcawl is the most likely 'new one' in my opinion. Its got some new road infrastructure, and plans to build a new clubhouse behind the 17th, that gives it, two nines, practice ground, better crowd movement within the\last few holes and moves everything nearer the main road. Porthcawl is very near a motorway junction and has 4 good qualyifing courses: Ashburnham, Pyle, Pennard & Southerdown plus a plenty of hotels (The Celtic). The course has staged the Amateur more times than any other course on the AM rota that has not staged the Open. New Plans will stretch it to over 7 as well. So its got the pedigree. It might be a bit tight for viewing in places, but they were worried about Hoylake for that reason and it passed the test. The R & A 'like' the idea of something South West and something Welsh.
Kingsbarns I think is a bit tight in places for viewing and too near St Andrews. Dornoch too remote, Saunton is hard to get too, RCD a possibility if it goes back to Ireland, and Portmarnock too. Likely Portrush though if they go to Ireland.
The Open was considered to go to Wentworth about 50 years ago and Michael Bonnallack was in favour of it going inland then. I dont think he is now though.