Slayer tower has already been implemented for a long time. The only thing Onur is probably doing is making the npcs walk. The npcs there need item requirements which only Ryan can do. On top of that, slayer tower will not be released without Priest in Peril and going to the KQ is pretty much pointless without barrows.
The only thing regular devs can really do is fix shops, add npcs, fix doors, and drops. Not much else.