SFS, good question. I used to work on simulators 20 years ago, back when computer generated imagery on flight sims was fairly new. I remember being sent to Evans and Sutherland in Salt Lake City for training once and seeing the prototype for the then new CT5 imaging system (boy that really dates me
).
I would imagine that maintenance could be a problem on older sims. Recently produced sims for older aircraft types wouldn't be problem, but sims produced with older computer technology could be increasingly difficult and costly to maintain. I can't imagine what it would be like to try and maintain a sim produced 20 years ago.
For airline pilot use, updating sims with newer computers and imaging systems can be cost justified. For example my first job after training, was updating a South African 747-100 sim that had a "moving camera over a model" technology that we replaced with a computer imaging system. We updated the sims main flight computer also. But for commercial ventures like selling time to the general public on an older sim, maintenance might be a problem. It's a great idea though.
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Safe flying to you...