It seems to satisfy all (I prefer 3 AA in rear), I--were I a designer--would spec out a single AA cell in the head lamp, wired to a removable 2 AA pack in rear with removable middle strap. (This would allow 1.5 volt or 3 cell 4.5 volt. This would allow a feeling of extreme light and balanced feel in the 3 cell mode, or a super light and portable 1 AA mode.) I also would include two posts (with covers) that one could alligator clip a 6v toolbelt battery pack onto. (I don't prefer proprietary attachments, since a 6 volt lead acid battery might work fine for some people.)
This would take a sofisticated controller for to handle a wide range of voltage power.
Personally don't think boost controllers are ever efficient. http://www.prc68.com/I/LED.shtml I throw lights out that don't get 9-12 hours of good light. I prefer a tight beam as human eye can only focus on 3 inch diameter circle anyway. [Details, though, is my profession.] Flood has its place, but is generally too inefficient for a mere battery powered machine.