Is Infernal Darkness more popular than EDHREC considers it to be? It’s certainly never going to be a bulk rare again, simply from the price benefiting from very old set’s supply drying up. I wouldn’t go out and rush into buying this card, but if you have any around, I’d definitely look to hold them long term. Contamination is probably strictly better, as that cumulative upkeep of Infernal Darkness can add up rather quickly. But in the format that Infernal Darkness would ever see play in - Commander - having another mana denial card in a Mono-Black control deck’s arsenal never hurts.
While not on the Reserved List, it's doubtful that Infernal Darkness will be reprinted due to the Cumulative Upkeep requirement. Contamination is more likely to see reprint, but like Infernal Darkness, forcing all lands to tap for nothing but Black mana doesn't seem like something Wizards of the Coast really wants to bring back.
Investment Window: Long-Term
Risk: Medium, but Low if you have copies you buy at under $1 or already have some to hold.
Price Target: $3-5+