With a fairly complete existing line of 40K rpg's, and a cream of the crop License property in Star Wars, it really doesn't seem likely that there will be a new 40K RPG line any time soon. But I enjoy speculating on what such a new game would be about, if it were ever to materialize. So, this is more "Wishing Well" than "Crystal Ball" territory, but--what the heck!--its for the Fun of it after all.
I like trying to pick a candidate for a new line out of existing Games Workshop games that don't already have rpg incarnations. A couple of candidates come readily to mind:
NECROMUNDA: Maybe not those exact gangs, but I like the idea of an rpg centered in the grungy, violent underbelly of the Underhives. Seems like it would be easy to do, basically being a low power equivalent to Dark Heresy, with a lot of similar types--(break out that Book of Judgment!) only with a very different theme. Gang building for a Player Character group would be similar to the undertakings and ventures of Rogue Trader, just grungier, and grimmer. In the dark, sort of. I think this would appeal to gamers who like the 40K universe, but squirm under the oppressive Authority present in most of the other game lines. But, without the soul-sucking eldritchy horror thingies of Chaos hanging around waiting to eat you, as in Black Crusade.
I know this would be an easy sell to any of my gaming groups.
TITAN LEGION: Mechs! How can you go wrong with Mechs? I mean, I think the fever-craze fascination with big walking roboty tanks has slackened off, but I'm sure there's still plenty of interest still active in the gamer community. Playing the crew of a Titan seems like a natural fit for most gaming circles, and you would have a variety of sizes and scales to work with. While there's plenty of canonical antagonists to fight: everything from Chaos Titans to Tyrannid Bio-Titans to Ork "Junkhemoths" to Eldar to...you get the picture, I prefer a slightly different idea. There are lots of "Cyclopean" and "Monolithic" Xenos ruins scattered around the existing game line settings. That's part of the juicy Lovecraftian atmosphere that FFG has injected into the games (and one of the things I love about them!). These are usually presented to evoke the flavor of Great Old Ones and unfathomably powerful but extinct (we hope) Xenos. But, what if some of those gargantuan thingies were still around ? You would need Titans to keep them at bay and preserve the Imperial Worlds from unimaginable Horror-ror! Yeah. Imperial Titans vs. Xenospawned Gargantuas! Mecha vs Kaiju, in the Grim Dark! That would be an easy sell to my gamers, too! In fact, it's such a juicy notion that I may just cobble together a campaign along those lines someday, with or without a dedicated game line to run it with.
...Then there are those non-human, non-Imperium options.
THE TAU: are too easy. Screw 'em. That'd be too close to playing "the Good Guys.". I've never liked the flavor of Tau, anyway. They just don't feel..."40Kish" enough to me.
ORKS: Now we'z talkin'! There's enough Ork material in Rogue Trader to design Ork PC's with, and you can glean enough out of the other lines' books to put together an all-Ork campaign easily enough. Heck, the forums are full of clever Mad Boyz GM's wot has done that very thing! Still, it would be a hoot to have an official Ork-centric RPG to play around with! First, I see it as some welcome relief from the unremittingly Darkish Grimlyness of the Grim Dark 40K setting. Come on! Orkz would be a delightful Beer & Pretzels game with outrageously bad accents, pizza and likely too much beer at the table. Oh, sure. It might get old as a steady diet, but it sure would be fun for one-off game nights, every once in awhile. Maybe not a game line, per se, but I'm sure more than enough gamers would get behind a single core book, or something.
And, falling back on the Games Workshop games justification, there's GORKAMORKA to invoke! Angelis would make a splendid RPG setting!
ELDAR: Lordy. My gamer friends, they just LOOOVE the Eldar! If I brought up the idea of a new 40K rpg at most of my gaming groups' sessions, the first thing anyone would blurt out would be "ELDAR!" I know that there have been grumbles from GW pros in the past about "not playing xenos characters because they are too alien" yadda yadda. Silly that. And I've heard choruses of "The Eldar are NOT 'Space Elves!' They're NOT!" *foot stamp* Which is just plain silly because they clearly ARE "Space Elves" and everybody darn well knows it! I think it'd be more fair to say that the Eldar are not JUST "Space Elves," which would be true since they've developed a lot of distinctive flavor over the years. At least the folks I hear about from GW these days sound a lot less cranky about such things, so it might not be a problem anymore. 'Sides, again, there's plenty of material for playing Eldar characters in Rogue Trader and enough material scattered about the lines to make an Eldar campaign doable. It's just that, again, it would be nice to have dedicated sourcebook type stuff instead of piecing things together. I know an Eldar game line would be greeted with fists full of dollars! Admittedly, my grubby currency-clutching paws would be right in there with the rest.
Xenos role-playing gets a little thin, and very, very weird after that, though.
I think it wouldn't be too hard to put together a Genestealer game, centered around infected/infested/whatever humans turning into 'Niddy xenomorph wannabes. All you have to do is look at the rpg empire White Wolf made out of "playing the monster" with characters who have cool powers but must forever struggle to cling to their Humanity amid the darkness of their unholy lusts/appetites and... ah. You get it, right?
On the far fringe of Weirdness, I'm putting together some ideas for playing Tyrannid Lictors (in an all-Lictor group, of course), or maybe even some other 'Nid types, with the intention of running some Convention games one of these days.( PM me if you want to hear of my Madness, or share your OWN! mwah-ha-hah! etc.)
Had a notion for an all Mechanicus game too, but that winds up just being a variant of already existing materials. The Mechanicus is thoroughly represented in every 40K game line already on the shelves, so it doesn't seem like there would be much point in rehashing so much of it.
I did play with an idea for a setting for an all Mechanicus game, though. Trying to think out just what sort of setting you would find nothing BUT Mechanicus adepts and minions, and what kind of Antagonists would do them justice, without dragging the Chaos-tainted back again, I came up with the notion of an Archaeotech menace. Back in the Dark Age of Technology, certainly there were fleets of proud vessels that journeyed out in glorious fleets to do inscrutable Tech Age "stuff." And theoretically it's pretty certain that they ran into opposition and hazards "Unguessed At!" So, the setting would be a drift of ancient, shattered, wrecks of such ships, in drifts between the stars and scattered across a cluster of worlds like broken toys. There's undreamt of wonders in there, to be sure, but also terrible Heretical dangers. Hostile Machine Spirits and techno-abominations of all kinds lurk within the wreckage, along with scavengers from every race and Empire. Only the Mechanicus themselves could be trusted to explore such a realm of Wonder and Horror!
Unfortunately, you can't base a campaign on Archaeotech without letting the PC's get their hands on Archaeotech, from time to time. And you certainly can't trust Player Characters with Archaeotech! In no time Game Balance and the Imperium's status quo become things of the lost past. So. yah. Maybe not. Still...it feels like there's a game in there...somewhere.
So, those are my Speculations. So far. Just for the fun of it!