To me, the most logical next item to be produced would be a 22k, as they've infected the entire system (almost), though the cost of producing a 3-car set would be prohibitively high. Having said that, as they are still only at the start of their working lives, they will be around for many years (yawn) & hence a number of re-runs over the years would probably be required as these will be the only trains that people will come to remember. Things like 121s are already history & hence already the number of people that they mean something to is starting to diminish if were are brutally honest.
Personally As & Cs don't mean anything to me as they'd all finished by the time that I discovered Irish railways, so I'd almost be inclined to wish for something like a 2700 railcar before a Metro-Vic, though I probably would purchase a model of an A or C if one became available having travelled behind A39 on a tour, but then the model would have to reflect it in it's preserved condition.
Yes I'd be interested in 4 wheeled freight stock, but the only thing that concerns me is how they'd be represented. Irish freight vehicles became notorious for being extremely heavily weathered - something that is hard to represent convincingly & if done poorly I find a total turn off.
My top 5 wish list:
1 4wd Cement bubbles
2 4wd Beet wagons
3 2700 railcar
4 4wd ballast wagons
5 4wd ballast brake / plough