What if Prestige...

I very much like the idea of gaining a 5th perk slot when you prestige, and gives people a reason to. I'd like it a bit better if it was available to both killer and survivor though. You have a very similar idea I had, where getting to Prestige I made the 5th perk a Tier I perk regardless of its current tier, and the ability to gain a tier when you prestige more. The 5th perk could initially be locked to one of that character's unique perks, with the option to expand and include generic perks (but never teachable perks).

Perhaps instead of having a boosted T3 perk when you get to Prestige III, each time you reach Level 50, the 5th perk becomes boosted (something like half a tier), so getting to Prestige III, Level 50, grants you a boosted T3 perk.

Alternately, just have the 5th perk be boosted when you reach Prestige III-50. For your Devour Hope example, it could have varying effects, such as require 1 less token to mori survivors, extend the cleanse time by 25%, make the totem blend in better with its surroundings, etc. I think the boosted aspect should just be a slightly enhanced perk, not just an additional tier. I can make several suggestions for boosted perks.

KILLERS (part 2 of 2)

Trapper
Unnerving Presence - hides notification for 5 seconds
Brutal Strength - generators regress an additional 1%
Agitation - grants the ability to bump survivors out of the way while carrying a survivor.

Wraith
Predator - scratch marks linger 2 seconds longer
Blood Hound - fresh blood stains are extremely discernible
Shadowborn - grants 10% resistance to blinding

Hillbilly
Enduring - grants 10% resistance to being stunned
Lightborn - 10% recovery from blinding
Tinkerer - 5% speed boost when triggered for 3 seconds

Nurse
Stridor - grunts of pain happen 10% more often inside terror radius
Thanatophobia - penalty applies when a survivor dies
Nurse's Calling - reduce terror radius by 25% when survivors are healing

Shape
Save The Best For Last - tokens can be granted after obsession dies
Play With Your Food - gain tokens from losing any survivor
Dying Light - other survivors receive penalty while obsession is in the dying state or on the hook

Hag
Hex: The Third Seal - each affected survivor grants the killer a 3 meter bonus to aura reading
Hex: Ruin - Hex Totem becomes 50% darker
Hex: Devour Hope - Hex Totem becomes 50% darker

Doctor
Overwhelming Presence - hides notification for 5 seconds
Monitor and Abuse - additional FoV increase
Overcharge - successful skill check will still regress generator

Huntress
Beast of Prey - Takes 5 seconds longer to lose bloodlust
Territorial Imperative - reduces range to 28 meters
Hex: Huntress Lullaby - Hex Totem becomes 50% darker

Cannibal
Knock Out - while in the dying state, survivors suffer from blurred vision and 25% reduced crawling speed
Barbecue and Chili - auras revealed for 6 seconds
Franklin's Demise - destroys one add-on per item

Nightmare
Fire Up - grants bonus for EACH repaired generator
Remember Me - obsession becomes affected by Remember Me
Blood Warden - triggers once an Exit Gate is opened

Pig
Hangman's Trick - sabotage action becomes 50% louder
Surveillance - effect lasts 24 seconds
Make Your Choice - cooldown reduced to 45 seconds

Clown
Bamboozle - ability to block a second vault location for 50% of the time
Coulrophobia - hides notification for 5 seconds
Pop Goes The Weasel - time extended to 45 seconds

Spirit
Spirit Fury - stun effect reduced by 50%
Hex: Haunted Ground - reveals all survivor locations for 3 seconds when cleansed
Rancour - Interactions with the obsession trigger when the hatch is opened.

Generic Perks
Bitter Murmur - range extended to 24 meters
Deerstalker - reveals crouched survivors auras within 8 meters of the dying survivor
Distressing - bonus 2% terror radius
Insidious - no terror radius for 5 seconds when starting to move.
Iron Grasp - stuns will not free survivors
Hex: No One Escapes Death - Dull Totems become 25% darker; when triggered, the Hex Totem gains an additional 25% darkness
Hex: Thrill of the Hunt - effects no longer tied to a totem
Monstrous Shrine - 5% reduced unhooking and healing speed while in the basement
Sloppy Butcher - adds a second stack of Mangled
Spies from the Shadows - stillness crows show up 50% sooner
Unrelenting - increases lunge range by 10%
Whispers - Entity's voice becomes louder when facing in the direction of a survivor, 45 second cooldown

No. If you're gonna boost 1 perk you'll have to rework the entire game(which is already broken as is). There will be an unfair advantage vs people who started playing a few months ago. Prestige never unlocks anything except cosmetics/titles for the player to show off in any game. It should stay that way.