In ARR we've used both 'machine' and 'machina,' the former in a more general sense, the latter to refer almost solely to Garlean technology. As the former is more widely seen throughout Eorzea, we're probably going to go with the soft 'sh' sound for machinist. I'd like to go into a little more depth, but the evil eye Oda-san is giving me right now has me frightened for my life, so you'll have to wait for further details.