I wouldn't really compare Keaton to Conroy, since while the latter does do some guest roles (John Grayson, Thomas Wayne, the Phantom Stranger, etc.), he still gets cast as Batman on other projects, while Keaton hasn't voiced Spidey in years.
Granted, I'm not actually upset about it, since while I do miss his Spider-Man, and I do think Marvel in general doesn't show The Spectacular Spider-Man (or any cartoons from the past) the respect it deserves like DC does with B:TAS, I do like that they keep putting him in related roles in newer Spider-Man projects. His voice acting career has also blown up A LOT since Spectacular, so I get to hear him in tons of other cartoons and games.
Now, depriving us of Steve Blum's delicious Goblin voice is the REAL crime here, and deserves far more outrage and protest.
Going by its effects (gray paleness and hardened skin) plus the name of gravedust, I'm guessing it's something directly related to Tombstone (you know, the spidey villain with gray/white skin and hardened skin who usually gains his superpowers via odd chemical processes)
It could alternatively be a vague distant counterpart to MGH (Mutant Growth Hormone) the go-to "mass-produced drug that gives people some superpowers at a incredibly terrible cost".
"All you Fascists bound to lose."It would be TOO cool if they added in a Black Cat, Prowler, Miles Morales, Spider-Ham and Venom as dlc. They don't need to have their own unique story just their own combat/play style, weapons/gadgets and finishers as a test run for future installments. I can already see Venom suffocating and eating mooks brains (probably off camera anyway).
Age is not merely hardship, but chapters of them.

That sounds like business than anything else, but I digress
I don't recall the Arkham putting so much emphasis on combat.