seeing as we're going off the sins as a general game mechanic, i think the sin of Pride makes a perfect addition to end-game. specifically, this system would help address the issue of "valuable" items to be stolen and fought over.
the Pride system would revolve around the creation, defense and theft of Banners, Tapestries and Engravings. these Items would be incredibly expensive to create, and would generate a small buff to all areas covered by the town claim or to the members of the town upon which They are displayed. as befitting an Item of true Nobility, Pride Items would be carryable objects only and would never fit inside a small and cramped backpack or rucksack.
to prevent it getting out of hand, the boost would have to be small. the first Pride Item for a specific buff would give a 5% boost, while the second would give 2.5%. the cap would be 10% reached at infinite Pride Objects, but the majority of the boost can be obtained with as little as three. Pride Objects themselves wouldn't be the only cost, Display Stands would need to be constructed for each Pride Item for them to give a bonus.
Banners would give combat related buffs, Tapestries/Engravings would generate industry/production related benefits.
~Display Stands~
Banner Stand: outdoor constructed building. may not be built within 5 tiles of another non-liftable structure. holds one Banner.
100 oiled boards
200 planed boards
400 bricks
20 iron poles (5 bars of iron each)
20 iron fittings (1 bar of iron each)
Tapestry Mount: indoor constructable item. must be built on a wall. holds one Tapestry.
100 oiled boards
200 planed boards
200 stone
400 bricks
20 iron hooks (1 bar of iron each)
~Pride Objects~ - during the construction of Pride objects, relevant skills will determine the chance of successfully building a material into the object. materials will not be lost, but high appropriate skills will drastically shorten the construction time.
Banners
Banner of the Exiled King (thread and needle to create)
+5% damage done in combat by town members for the first displayed Banner
100 sea island cloth
200 indian cloth
400 embroidery thread (stackable up to 10, sort 1 cotton ball -> cotton wisps, spin at loom -> 1 embroidery thread if successful, success based on thread and needle skill)
Banner of the Valiant Knight (thread and needle to create)
-5% damage received by town members for the first displayed Banner
100 sea island cloth
200 egyptian cloth
400 embroidery thread
Banner of the Wounded Message Runner (thread and needle to create)
+base movespeed. the increase in speed will not exceed wander movement, and it will not increase the speed during forage, wander or run movement types. nor will it increase movement speed while using combat stances.
300 egyptian cloth
300 indian cloth
400 embroidery thread
Tapestries and Engravings
Ode to the Bountiful Harvest (Tapestry: arts and crafts to create)
fields within the town claim receive +5% of total plenty (after s/c bonus is summed in) when planted for the first tapestry.
100 sea island cloth
400 strips of indian cloth (cut with iron scissors (2 bars of iron to produce), success based on arts and crafts skill level, produces 2 strips if successful)
400 embroidery thread
Tale of the Spring Planting (Tapestry: arts and crafts to create)
fields within the town claim receive +5% speed when planted for the first tapestry.
100 sea island cloth
400 strips of egyptian cloth
400 embroidery thread
Story of the Industrious Worker (Engraving: hammer and nail to create)
maturation items (coal piles, plank piles) require 5% less server ticks to mature when built on town claim for the first engraving.
100 a face in the dross
200 decorative wood carvings
100 oiled boards
summary: a horrendously expensive game of capture the flag with useful but non-game breaking buffs for the hoarders of flags. to have multiple of these objects would be a very grueling construction process that would have to be planned for from the start and would in general keep the hardcore "endgamers" busy building and fighting over them for a good long while. all actual values are best guesses from me what wouldn't be out of hand, but obviously none of the values are set in stone if this were to be adapted for salem.