Suggestion is simple.
Like, if you get Demon task, it doesn't matter which ones you kill, exp depends on Hitpoints(excluding Bosses like SDC, GWD and etc.) and number of demons you have to kill is 150 - 200, you can choose between easy ones (Lesser Demons) or harder ones (Black Demons). Same could go for Dragon, Spider, Giant, Undead/Ghost or Boss Task.
For Boss task, implementing numberic choosing between 1 - 10, would make tasks not only longer but more interesting to do. Group Bossing would definitely get more popular around slayer master ing. King Black Dragon remove from Boss task list and land it in place alongside Dragons(it's not very hard task anyways). For Spider task, Kolodion could be placed on list as well since you can kill easily with only 50+ ranged and 37+ prayer. Undead/Ghosts might have Spectrals and Revenants as count too, but up to 100 per slayer task, so players won't farm them for too long. As for Giant task, Fire, Hill, Moss or Ice Giant, doesn't matter any can be done. Other tasks can be left untouched, unless any ideas I forgot. Add some feedback to it, much appreciated
Have a good day everyone.