Effigys- Since they cost 600 prestige points each, and at prestige 10 you get over 1,3k prestige points, therefore they should give around 500k xp in a skill of your choice. And yes, they should give xp to dung too, but its your loss since you wont get any dung pts for it.
Slayer shop- Maybe add some more items in the shop like, virtus and pernix since they are to hard to get from dung.
Prestige shop- In this shop you could add the chaotics since at dung you would most likely buy primals. And maybe make the new max prestige to 15-20, this would mean shields and weapons.
Runecrafting pouches- They should be added to the game because atm runecrafting is too hard to do, its around 23k xp per trip at 77-99, which means 13,034,000 is 99(sort off) 13,034,000/23,000 = 566 runs ( that is over 10k rune essence).
Max cape- Have all skills to 99. This cape shouldn't be too hard to add, but its not necessary just a fun cape for proving your maxed account.
Completionists cape- This would maybe require:
All 99s of course.
And maybe something like this to unlock it, and after that it costs 100m per cape.
500 Pest ctrl points.
1k slayer pts.
Killed all bosses atleast once.
Have prestiged atleast 10 times.
Barrow gloves.
Fire cape.
This about the comp cape is just a fun thing i thought about not sure if its even possible.
~~Chris~~