The feasibility of non-combustion gas turbines in nuclear reactors

In a discussion about nuclear reactors, a discussion subthread about gas turbines as energy converters ended with this late-arriving statement:

Non-combustion gas turbines are not proven. They're mostly in pilot/research stages. You say that the conditions in non-combustion lower temp operation are more reasonable than in higher temp combustion gas turbines, but the fact that they are not commercially competing with Rankine steam cycles, even in the higher temperature regimes, should caution us not to trivialize the engineering/commercial issues.

The one-week period for comment on the post ended before I could write a response.

What's missing from this analysis?  Let me lay out the pieces: