I would favor making the Ninja Backpack an item enhanced by other equipped exotic gear, similar to how sets behave now. Here's a sample properties list:
3 exotic items equipped: +10% weapon stability and accuracy
4 exotic items equipped: +10% resist all damage
5 exotic items equipped: +10% weapon damage; ammo now regenerates in equipped weapon magazine at 10% per second until full
EDIT: increased requirements to account for exotic weapons being counted in activation properties.
Agreed about helping solo players. Somebody in a different thread had a great suggestion: being concealed from hostile pulses (like the Scrambler pulse mod).
Other ideas, from less to more ridiculous:
- No damage from falls
- Cannot be targeted by enemy skills
- Decreased detection range by NPCs (or undetectable if walking, not taking damage, not shooting or deploying a skill, and with no skills active or on cooldown)
- Invisible if in cover, non-rogue, with no skills active or on cooldown and not moving/shooting/deploying a skill
I would caution against making the Ninja Backpack an over-specialized one-trick pony (e.g., DZ-soloers only) since that will keep the item in its present "deconstruct-on-sight" status for the vast majority of TD players. It should receive a sizable buff so that it leaves its exotic-trash status behind once and for all.