I do not know if there are any "proposed" missions, whatever that means. Seems to me that it's quite achievable given a modest effort. And interesting from my perspective. Life support would be the challenge. To the right NEO, Delta V has to be somewhat less than a lunar mission, no lunar landing or takeoff. I'm certain that NEOs with mission round trip times in less than 6 months could be found.

The problem is...if it's NASA that does it, the mission will be gold plated. Totally new life support, totally new hab modules, avionics, propulsion, etc. All buried in tons of ISO9000 documents. This "simple" task burdened with govt requirements will become quite expen$ive.

-p