I think almost anything from the mid 50's is commercially viable nowadays as we have the RTR locomotives out there in the wild and the odds of a C Class are not insignificant (a locomotive that was withdrawn before IE came into existence). I entered the hobby wanting to do only 90's IE stuff. Then along came those delightful silver and green A's, so I bought A1, A30, A42 and A46 and then as I believed that the stock will eventually become available I bought B121 and B135. I strongly suspect I am not the only one who is now looking at earlier stuff too. It will take some time but I am personally fairly confident that this era at least will in time be well catered to by IRM. I do not believe, for example, that 3 packs of open plank wagons or 2 axle covered wagons wouldn't sell very well at this stage. They even have an advantage over bogie stock for those tight on space. This "moving back in time" phenomenon happened with GB outline modellers too. I suspect that we will definitely see bogie coaching stock from the mid 50's as this also had a long life into CIE and in some cases IR days, like the A's.