You can scale Reaper bleed DPS pretty high now

PoB: https://pastebin.com/kdGKVDMG (note that I added stuff that doesn't work in PoB to the bow)

While watching Ventrua stream Reaper I was theorycrafting a bit. If you go for a +1/+2 support gems bow with an essence of fear on Reaper you get to pretty good bleed DPS. In my PoB with endgame gear it's about 5.5M bleed dps. Without awakened gems and when dropping the entire cluster setup it's still almost 4M bleed DPS. You can probably scale it even higher if you go for more SC strats.

I think scaling Reaper with bow could be really good because you can use Ensnaring Arrow for the bleed. The only thing that I haven't fully solved yet is the fact that it only has 60% chance to bleed, which is not great(but still manageable if you have a second Reaper setup with Second Wind).