So, I was playing around with the strong soft shackle yesterday and realized that its design lends itself to a "soft halyard" type construction.
The interesting feature of this shackle design is that the tails exit on the same side of the knot as the standing parts. What's to say that we have to bury the tails into the standing parts?
What happens if we make one tail longer? Maybe significantly longer, then bury the other (short) tail into it?
Well, now we have a soft shackle with a spare long tail that we could do something useful with!
I guess you could do this at the end of a halyard, but it would be mildly annoying to build the button knot with such a long tail (the rest of the halyard), and if the shackle eventually failed for some reason, reconstructing it would shorten the halyard by several feet.
One interesting use would be to thread 72 diameters or more of the tail over another line. This would give us a soft shackle that could be slid to any position on the line, but would stay put as soon as a load is placed on it (something like a whoopie sling)!
This type of construction would yield a strength of somewhere short of 100% (of single line strength), but might be useful for something like a backstay pigtail.