It's an interesting idea, but I don't think it's likely to be implemented.
An overpowered weapon like would be fine against NPCs, but it wouldn't be fair to other cmdrs. The only way I could see something like that working in Elite is if there was a significant opportunity for others to fire at the weapon during charge-up, to trigger a premature detonation, which would engulf the ship with the BFG and destroy it. Also, I'd want to see a RNG for the kickback to be say 1-3 km, so that there's a fair chance that the ship would also be engulfed in the singularity.
Overall, I really don't see much of a chance of a weapon like that being added to Elite. It's too powerful. There are already complaints about the station's weapons being overpowered. There's not much fun to be had with a single-shot kill weapon, at least for the other players and there's no skill involved, unlike a railgun, which needs precise aiming.
And what happens if it is detonated near a station, which is inevitable? Does it destroy the station or just the nearby ships? If a lucky shot gets through the mailslot, do all the docked ships get engulfed? I just don't see this as a feasible option.