Calling BT SF in any sense of the word would be a stretch of monumental proportions. Its static nature is antithesis to that literary tradition. Children make the mistakes of their parents, over and over and over ad infinitum and it's never once asked why that fundamentally seems doomed to happen. 40k was never SF, is not fundamentally different from BT in any notable regard, and it's high fantasy, pure and simple. It might be high fantasy with laser guns, but contrary to the common mistake made in identifying these genres, the fantasy/SF divide was never about the nature of technology, and since magic is by definition technology -well, usually-, that's not even a workable definition in the first place. Star Wars is textbook Campbellian fantasy. How to Train your Dragon is, at least in my opinion, textbook science fiction. It doesn't matter than the former has space ships and the latter, well, dragons. These genres are not defined that way, but are instead defined the same way all genres are defined: the nature and progression of the fundamental plot that the characters progress through and the fundamental nature of the characters themself.
Noted science fiction author David Brin offers a brief exploration of the difference here. Science fiction is, at its core, exactly what he calls it: the literature of change.
I note this because there's just no way in which these two franchises interact at the genre level. That just doesn't come into play here, because at heart, they're the same genre, and they deal with the same elements and the same basic rules, exactly the same basic rules. So what if the phenomena in 40k include the psychic? That either just means the laws of physics are a little different, or that 40k's civilizations have discovered something, a technology, a method, that BT's haven't, just like BT has discovered FTL, which is either reliant on physical rules that don't and can't exist here in the real universe, or is simply reliant on the discovery of rules and associated phenomena that we have not discovered. That doesn't mean there's a genre difference here, or that one is science fiction and the other is not.
In fact, these two universes both exist and persist precisely because neither is science fiction. What would happen if either did permit change, real, lasting change, change so fundamental that it allowed characters to not only question, but even to rewrite the fundamental premises of the story? This is the sort of story that neither franchise allows, because for better or worse, the creators have decided that stagnation and endless repetition of the mistakes of forebearers is what maintains the ideal universe for their purposes. Sooner or later even the Republic of the Sphere will come crashing down, and oh hey, WAR TIME folks. That process has already begun, and anyone here could have predicted it long before the HPG network collapse. I certainly don't say this out of scorn, well not much scorn anyways. I have real fondness for BT, and certainly no animosity towards 40k (some of its fans perhaps, but that's true of anything). Nevertheless, they are what they are.
A real science fiction franchise even entering this discussion would turn this entire comparison on its head, because the very act of introducing them would be to entertain the possibility that the fundamental premises of 40k or BT could become malleable, or even able to be thrown in the dustbin altogether, to the effect of, well, who the hell knows what. Imagine Trek coming in and having to entertain the possibility that every aspect of the warp might be amenable to scientific investigation, and every problem a solution via technology and imagination. Imagine Stargate coming in with hard-learned lessons from generations past, lessons about not making the mistakes of their forebearers when it came to self-made and self-proclaimed gods and demigods that might influence the status of everyone from the chaos gods to the Emperor and fundamentally upset the universe (the Tau'ri did basically get sick of the Ori and wipe them all out with a device the size of a fruitcake after all). That is what genre differences look like.
BT and 40k meeting doesn't require changing premises of either universe. There's no difference in the premises of the universes. So you certainly can't say that that's why one side or the other is going to triumph.
40k is going to win here because it's just better at doing what BT does than BT is, at least insofar as making mean, war-making, classic fantasy civilizations (new and improved with pewpew laser guns). 40K has older, bigger and meaner versions of the same thing, plain and simple.
Edited by Catamount, 11 June 2015 - 03:35 PM.