Kipling was… “the first modern science fiction writer” — John W. Campbell, editor of the seminal Astounding magazine and pioneer of hard science-fiction.

What Kipling was doing in “With the Night Mail”… “had never been done before. There is no such subtlety in the contemporary proto-SF of H.G. Wells and Jules Verne. I think we may safely credit him with inventing the style of exposition that was to become modern SF’s most important device for managing and conveying information about imaginary futures”. — “Rudyard Kipling Invented SF!”, by Eric S. Raymond.

“With The Night Mail”… “anticipated the style and expository mechanics of Campbellian hard science fiction fourteen years before Hugo Gernsback’s invention of the ‘scientifiction’ genre and twenty-seven years before Heinlein’s first publication.” Eric S. Raymond, A Political History of SF (2000).

“With The Night Mail” is… “an amazing tour-de-force of inspired genius […] the sort of thing that Verne or Wells would never have dreamed of doing […] Kipling, in 1905, is doing things that science fiction as a genre wouldn’t achieve until Robert Heinlein arrived in the late 1940s.” — Bruce Sterling.

Kipling… “is for everyone who responds to vividness, word magic, sheer storytelling.” — Poul Anderson.

Kipling was… “a master of our art.” — Gordon R. Dickson.

“He was a superb and painstaking craftsman, the most completely well-equipped writer of short stories ever to tackle that form in the richest of languages.” … “”With the Night Mail” is an astounding vision … his influence on 20th century SF writers was probably greater than anyone else’s, except Wells … he was a master at making the fantastic seem credible”. — John Brunner.

“When you read Kipling, you’re there, [he] builds a total sensory impression that surpasses the language” [which is partly why he will never be taught in schools] — C.J. Cherryh.

“what a good writer he was … the work is superb and he could make words sing. [On looking into the leftist political claims that had dissuaded me from reading him,] I found that most of his supposed sins had been vastly overstated.” — George R.R. Martin.

At SF conventions… “I found that so many SF writers could see his sterling merit that I felt vindicated” [in my early love of Kipling, despite my mundane Eng. Lit. teachers who ignored him] — Anne McCaffrey.

Heinlein was also strongly influenced by the “Night Mail” style and viewpoint, but I can as yet find no quote from him on this point.

The 1980s anthology Heads to the Storm (ed. David Drake) features stories by later SF and fantasy authors, all inspired by Kipling, along with many tributes.