While I don't want to argue against your main point, that enlightened rhetoric has changed the statistical emphasis of popular preaching, I feel compelled to point out that higher theology and literature have always understood the conception Ingersoll may have helped to overthrow to be a simple misinterpretation.
One need look no further than Dante or Milton to be confronted with the fact that
the gates of hell stand open. In
Paradise Lost the key is held by Sin, who, once letting them gape wide, finds she has no power to pull them shut again, and proceeds with her son Death to build a vast bridge to earth. In the
Inferno this opening is attributed to the Son, in the course of the Harrowing.
This opens up yet another point. Theologically, hell may have once represented a place which was free of God, the dreary Sheol of Hebrew myth, but this is no longer the case. With the nature of God being eternal, having become human he has always been human, having died he has become eternal Death -- "the lamb slain from before the foundation of the world" -- and having visited hell he resides there eternally.
God is the
fire.