If we remove (eg) the competitive grant system, will researchers slack off?

I’ll bet some would and some wouldn’t. See Einstein and how he was working on relativity (at least at the beginning).

If this trait is genetically detectable, it would presumably be a selection criteria for MSI-1. If it is based on nurture, presumably the necessary conditions would be part of the indoctrination for MSI-1. Finally, if it cannot be anticipated, presumably MSI-1 would use post-facto selection (i.e., raise and train more than 10k candidates, keep those that “work” and let the others do other stuff.)

Also, there are likely other motivational elements that would work in a MSI-1 (at least in my view, the selection and training and indoctrination implicit in the OP’s suggestion would be very different from any group I am aware of in history). And stuff like peer recognition and the satisfaction of a job well done are huge motivators in some cultures.

Also, remember we’re seeing this with culture-tinted glasses: In the west pretty much everyone is focused on a carreer, family and the like; the few who aren’t are seen as “slackers”, “hippies”, “weirdos” etc. Even if not subscribing to that cultural subtext rationally, it’s hard to prevent the unconscious associations of “no care for money=status” => “no motivation”.

Moreover, and this was part of my idea, I think there may be something to the idea behind structured procrastination (.com). Which is to say I don't really know. What I do know is that I'm not very single-minded and there is evidence it is not a common trait.