Slide vs (Dup loop and slide) ...

[puzzledpaul]

Imo, the simplest way of creating a dupe partial eloop is to select relevant edges then use either

Edge > Bevel > 0 for a single extra edge sequence
or
Edge > Extrude > Normal > 0 for extra edges on either side of the selected geom (no bump)

To select the duped edges (*in a 100% guaranteed manner ) select the adjacent faces on the relevant side that sliding will take place, convert to edge selection, deselect unwanted edges ... and use slide.

Body | Cleanup seems to sort out the unwanted stuff ... provided the original edges aren't modified.

Yes, I'd have thought a dupe option for slide would be useful ... trying to remember whether the Clacos plug of many yrsago had this dupe feature ... but memory fails me atm.

Big issue (imo) re implementation is how to tell wings what side of the original edges user wishes to slide the dupe ... and select those relevant edges.

Various approaches would, no doubt, surface if there's any serious possibility of this being added ...

Yes, was me that originally raised the simultaneous 'pinch / expand' option of a pair of eloops (one either side of a 'main' one) ... I'd been adding control eloops to the trailing edge of an aircraft wing ... and such a feature would've been useful.

pp

*Can also (in e mode) tumble model and place cursor in centre(ish) of face on side that you want to slide, highlight ('duped' edge, then select.