I could certainly see more SAR locos being considered for preservation within the UK. I am impressed with what the Welsh Highland Railway has done with the NG15 loco, and it looks very much at home there.
It might be my stubborn nature on this, however, I think more needs to be done with the established narrow gauges within the UK first. Germany has many steam enthusiasts of their own, and lines like the Harz are still popular over there. Plus, railways like the Harz are relatively easy enough to visit from the UK to Germany, especially with budget airlines.
There would probably be more demand to build a narrow gauge line using Isle of Man locos and rolling stock in the UK than a continental-based one with metre gauge.
Apologies for the tangent, I know this thread is for new heritage railways in the UK, but I am surprised that Japan might not be considering new heritage railways as smaller branch lines are being lost in Japan as rural populations decline.