Yet another suggestion for [Blackthorne’s Battlegear] rework. I know there were plenty of them, but most of them were more focused toward straight boosts or adding farming utilities, not working around its unique style. The fact is this set might have a great potential, especially when there are only a few defensive builds. Unfortunately, right now it is an obsolete and totally forgotten since like… I do not know, Reaper of Souls release?
Non-class sets were mostly taken as a supporting fillers, but when Legacy of Nightmares had been buffed, it proved its power of possibilities. Just look how many Legacy of Dreams and Nightmares setups became high tier builds. So IT IS a high time to give our poor Blackthorne a love it missed for so long! Because what is more satisfying in Diablo than seeking a new ways to slaughter those foul demons? 
I hope I did not bored You with this overlong introduction, did I?
So this is what I suggest:
> (2) : Character becomes immune to [Specific/Most/All?] monster affix ground effects.
In this setup it definitely MUST be a first (or 2nd - point 2. in Overview) bonus because it is not too powerful to make others class sets overpowered, yet further ones in fact are.
>(4/5) : Reduces [All/Non-Elite] Damage taken by [50/60/70/80/90?] % when there are no elite pack within [20/30/40/50?] y range.
Sorry if it sounds a bit like Unhallowed, but I do not have any better idea right now and without it one could get oneshotted by a single trash mob.
Those numbers are just an overview.
>(6): Getting hit by elite’s pack affix increases Your damage by [XXXX] % and reduces all damage taken by [XX] % for [5/10/15/20/30] sec, stacking up to [XX] times.
The best part of this rework. And quite a RNG I would say, but sounds no less fun. Basically this bonus puts into REAL use Blackthorne’s original bonus, turning it into a deadly weapon.
Overview :
1) It would be a defensive build, basing on kiting elite monsters far enough to keep 2nd bonus active, and close enough to keep getting stacks from their abilities. A bit like Vyr, but focused toward getting hit instead of damaging and faaaar more flexible in building.
2) The greatest problem with reworking this set is in its parts. Because of belt and neck + cubed Royal Grandeur it MUST have a 6th part and one of those parts converted into head/shoulder/hands or it will be turned into SLIGHTY overpowered hybrids.
Otherwise 2nd and 3rd bonus could be merged and some builds like Roland (because this one is the biggest thorn here for now with its 13k% bonus) would need to have their set bonuses swapped in order to avoid those damage boosts synergies.
3) Most of those [bolded] parts are for customization in order to preserve some kind of balance. Also in (2) may be turned into inversion instead of immunity, but personally I think it would be too much.
So…
This is only a starting design and any customization, suggestion or discussion is dearly welcome. But as I said: It would be nice to keep this set original purpose. 
In the end It is worth much more than rotting in the Hall of Shamefull Drops.