As a former legislative staffer (state level), my instinct is always to look for the subterranean motives behind proposal of such legislation.
This looks like a Democrats-only initiative, which means Harkin has no aspirations for its passage. That should mean he wants something from DOL which, as Kirk suggests, is ostensibly the outfit that should be advocating for participants' interests.
My hunch is Harkin's constituency doesn't line up well with DOL's; he gains nothing from extending its domain, & loses nothing by proposing creation of a 'competing' entity--and may gain indirectly from it. How? Since he sits on a body that oversees DOL, DOL may find it valuable to horse-trade with him concerning this issue ("we have a bill that may accomplish some/all of your goals; How might we persuade you to table your own initiative?")
I confess I haven't read the bill in detail, and my conjectures are totally academic. Still, my bottom line is that this dog barks, but won't hunt.
An aside:
Senator Harkin's website is...what it is. Can anyone find his Committee assignments mentioned anywhere there?