So it's just like the level syncing system in WoW where the zones have a minimum level, but mobs always scale up to your level?
Also, why should you be able to grind in Blackburrow well after the mobs turn grey? Because this sounds just like something for turbo autists, who don't want to experience new things and explore and just repeat once learned movements ad infinitum.
And what should those "increased rewards" be? Once you hit 50 in Blackburrow stuff like FBSS drops from there, too? That said, I'm not sold on the "bigger challenge more rewards" thing, because it was usually "bigger risk" in EQ, which was implemented as either "you need more people to be succesful" (aka raids), or "the geography/dungeon makes it more risky". Especially if you fuck up and may not be easily able to retrieve your corpse.
Whats the risk in your scaled Blackburrow? If you die you can just disable content scaling and drag your corpse to the entrance.
Corpses would obviously not be a thing in a scaling stat-based server. That kind of shit is tedious, not challenging. We're adults here, we need to treat players like adults who have lives.
Having the convenience of staying in Blackburrow a few more levels past its prime, while receiving reduced rewards, is the way to go. Obviously you won't get as good exp or loot as grouping in a level 50 zone, but you shouldn't be punished for playing where ever you are.
Increased rewards should be focused around stats and stats only; if you start adding in raw, inflated linear stats like HP/Mana/Endur/AC then it's a huge issue. EQ historically has only a few stats that are relevant, the rest are kind of... filler garbage that doesn't really matter. I'd argue that the only stats in classic that matter are AC, STA, HP/Mana/Endur and the class you pick's skill caps and spells available. How many times in classic EQ have you said, "Damn, I wish I had more AGI"?
The rewards should be proportionate to the content you are facing. If you choose to do Blackburrow at 50, you should only get rewards up to level 50 and they should have a higher chance of dropping lower level statted items. The zone itself should have modifiers that increase the base rewards and difficulty of the scaled-up NPCs that are proportionate to the modifier.
Additionally, I'd say that NPCs themselves need the ability to have a difficulty and scripted mechanics, so that not everything is a 'throw more NPCs/players' at it game.
I think there's this huge misconception that EQ, as it currently stands, is set up in any way mechanically to support this system. I am not proposing using EQ's combat or gameplay mechanics, I am using them as an familiar example.
What is the risk in a scaled Blackburrow? Not as much as a level appropriate zone where NPCs would have a higher base difficulty. The NPCs in higher level zones would award experience and loot proportionate to their difficulty.