I dug up a list of the DC ARCHIVES hardcovers of the Legion series so far, 13 volumes...
https://www.mycomicshop.com/search?TID=516741...the last one Volume 13 published in May 2012, of issues 224-233. Seven years ago!
So at 10 issues a volume, it would be about 5 volumes until they'd get to the Levitz/Giffen material in 284-306.
I think the natural break in the story for a 6th future volume would be containing issues 284-295.
And then the 7th containing 296-306. Issues 296-297 re-tells the Legion's origin, and therefore is the best to start a volume with. And 306 I think would end the volume on an optimistic note, with a great sense of completeness.
After that, getting into an 8th volume is tricky, because there's not a lot of great storytelling to draw readership to that volume. I was thinking 307-313, and then TALES OF THE LEGION (writer Mindy Newell, no longer Levitz, writing issues 314-325) in one volume, the last of the second series SUPERBOY/LEGION run. That would be 19 issues in one volume, plus possibly an annual or two. Maybe giving a generous amount of material in one volume at a fair price would make it more appealing.
And if DC wanted to do a 9th volume, begin with the LEGION third series (1984) with the Levitz/Giffen and Lightle issues. Although again, this is the point where the original issues are printed in a high-quality format, so it is not as necessary to reprint them in a higher quality format in a new edition.
But regardless, DC is still about 8 volumes away from completing the original SUPERBOY/LEGION second series run.
