Just random stuff I came up with, some are most likely too much to ask for. If you have any questions about anything I'll try to give you a more detailed explanation.
Misc
Something similar to the Boost Information client from runelite. http://prntscr.com/mnpmnt
Ability to add teleports to favorites http://prntscr.com/m9a2h8
Some sort of loyalty program, similar to the Login x consecutive days achievement. With useful skilling supplies for the ironmen
Clicking a skill should either bring up the skill info or redirect you to a forums guide
Pet booster scroll to the KOTH shop
Achievement shop with slayer sword 1-4 with different perks
Add a new compass if that's possible, with south, east and wests. For some reason swedes has a hard time learning the compass.
Add the ability to create slayer rings as a reward from the slayer shop, with the ability to teleport to the task. http://prntscr.com/mnpnny
Tortures are hella expensive, add it as a very very rare drop from hellhounds?
Make some poll/contest regarding a updated donator zone?
Add bank fillers
Change the color of rare drops message in the chatbox, not noticable enough
Right click to assign new slayer task option
Skilling
No idea why you can't ::empty while skilling anymore, but it's fucking retarded and should be reverted
Add rooftops, agility is too bland with only two agility courses Experience-boosting sets to the donator shop.
Wilderness slayer tasks (Krystilia). Krystilia tasks gives you more slayer points than regulas tasks.
Slayer cape/max cape perks (with the cape equipped, slayer Masters will give you the last completed task.)
Skipping a slayer task should give you a guarantee to not get the same task again
More items to the slayer shop. Such as herb boxes & gem bags for our fellow ironmen
Woodcutting guild, great way to introduce redwood logs or another best xp/hr tree
Add vorkath as a slayer task, similar to loco toro.
Add Arceuus spellbook and the ensouled heads for our fellow ironmen
Make sand crabs multi combat
More barrage/multi friendly tasks such as abyssal demons/nechs/dust devils, atm you can't get other tasks than hellhounds/black demons/black drags
