After seeing the "reaper of souls" career, when I befriended the Grim Reaper I was over-hyped. Then I realized that it was simply a npc career, I was so crushed. Then I got over-hyped for a second time when I learned the hidden reaping skill, then got crushed yet again when I learned that it was useless. I wonder if they ever intended a Grim Reaper life-state. Because when I moved him in, I realized that he only needed fun and social. That combined with the reaping skill, and the hidden "reaper of souls" career, kind of proves that they planned more for the Grim Reaper.
They gave us Grim's Ghastly manor in the past so I am hopeful that we will see more from the Grim Reaper. It could be fun to see the living or the working quarters of the Grim Reaper. He could see the lifespan of all the sims, when the mouse is hovered upon them, or add longevity to the Sims lives when bribed like you mentioned. There are countless possibilities.
Back in the original Sims, The Grim Reaper had the small halloween easter egg. If the household had Jack O lantern The Grim Reaper would ring the doorbell and run. It was so scary and fun.
Come to think of it we had plenty of interaction with the grim reaper.
In the Sims 2 university, we had the opportunity to call the Grim Reaper and resurrect the dead ones. That could also come back in a different form. It could be like the Sims 3 opportunities. But first we need the graveyards back. ( funerals are also needed) Grim reaper could locate the lost soul somewhere around the map, capture it similar to the ghost hunting profession from the ambitions, then bring the body and the soul together to revive the Sim.
Summoning the Grim Reaper to the lot, without a Sim dying would also be fun. They could bring back the grim reaper phone, or create an all new magical item to summon the Grim Reaper to socialize with him. Using this special item we could join the Soul Reaper career.
Grim Reaper's could be immune to all types of death except old age. When their time comes, they could simply turn to dust, leaving their scythe behind.
