USCIS has come out with a proposed rule on who can apply. At this stage, the public can still comment on the pros/cons of the rule.
Something to note: LPRs are not included in the provisional waiver benefits. In other words, spouses or children of LPR (Legal permanent resident or green card holder) petitioners will still have to go through the whole process overseas and wait overseas for their results according to this new proposed rule.
I am keeping an eye out for updates on I-601.