Twisted Engine
I respectfully disagree. These are "niche" aircraft, to the extent that they are tailored to a particular mission. A carrier who carries pax from Cat III to Cat III has a specific and well-defined need. In 3rd world ops, a runout classic 74 may pack in 500 souls but slurp Jet at hideous volumes. By definition, your question targets new aircraft, and new aircraft are prohibitively costly to other than first rate carriers. Also, you mention the lack of availability of "thrust" choices. Thrust choice is the result of cockpit selection, unless you meant supplying A/C with low peak thrust, which would be dangerous in the hands of marginal mission demands. Max thrust is an availability tailored by engineered requirements suggested by the operator, and Manufacturing safety and performance demands at minimum levels. You see, building an A/C with "smaller" engines to cruise economically at lower speeds would limit useful load and runway balanced length, etc. The market in used aircraft is wide open, and troubling in some respects concerning age, airworthiness. Customers buying dozens and hundreds of new A/C will always drive the new market, not marginal cash strapped operators with frightening line procedures.
From my earlier post, engines are irretrievably mated to airframes as a package, if you want slower and cheaper you'll need to choose another A/C, because putting small engines on an airframe that has load limits, is an invitation to disaster. "You'd like the weak donks? no problem, just don't fill the aft cabin with people." Oh-Oh.