I'm not a fan of disproportionate punishment, so no. It's eternity, dude. Ten years down the line, he'd still be in there. A hundred years, well after Lelouch has moved on to grander things than petty revenge, he'd still be there. A thousand years, a million years, after Creation has been left to crumble and the new titans go to find lost Zen Mu, he'd still be there.
Just a note on this - while this is a perfectly reasonable value to hold, it should be remembered that Lelouch does not necessarily hold to that. Even if V.V. didn't actually successfully kill Marianne, he did cripple Nunnally, which is probably something that would make Lelouch go 'eternity is not long enough'. Canonically Lelouch was willing to trap his father in the World of C for all eternity after he had attained V.V.'s Code of Immortality, so Lelouch probably wouldn't balk at doing this kind of thing against the right person.
The guys who can have the Ghost-Eating Techinque only recently started spawning again.
As I said "Reading that it functionally doesn't seem too much different from any other spirit-killing Charm" - other spirit-killing Charms exist aplenty, and I don't see anything in the Charm description that indicates it's any more powerful than any other spirit-killer. It's only an Essence 3 Charm. There's absolutely nothing about it that says it can kill beings that other spirit-killers can't. Really the only reason I can see that a Dragonblooded with Spirit-Shredding Attack couldn't kill a Primordial is because they wouldn't be able to survive long enough to do so.