In my youth 40K was only ever a passing interest, with its fantasy cousin proving far more of a draw to our gaming group, but my older self sees the Rogue Trader universe as a brilliant but flawed creation. Mostly I can happily continue to shun it and stick to my orcs and dwarves, until something like Axiom's astropath grabs my attention.
The setting's brilliance is in how it frames "medieval in space" as vaguely plausible, and hence allows table top battles between space-faring civilisations, without the technical levels being so mismatched that the only possible conflict is asymmetric. At least within the Imperium.
But you can only pull that "technology is religious mantra" trick once, so where does that leave our other standard races?
I like orcs probably more than most, but let's be clear - orcs are not a spacefaring civilisation (or arguably even a civilisation at all!). In orcish society there is none of the standing on the shoulders of giants that's needed for any sort of technological process. Let's be generous and say that their limit is muzzle-loading firearms.
Who knows how orks came to be spread through the galaxy from their home world, or even if they had a home world - maybe they were seeded widely by the Old Slann? When they travel through space now it's in the retinues of Renegades, or mercenary commanders keen to make use of their love of battle. Occasionally an exception individual will rise to lead a mercenary company themselves, but when that individual is killed or toppled the remnants of the company may well find themselves stranded on whatever world was the scene of their latest engagement.
So, orks have no space fleets or dreadnoughts of their own, and their vehicles (invariably wheeled or tracked) have a Heath Robinson appearance which reveal their cobbled-together origins and are highly unreliable.
The occasional wealthy mercenary my have carapace armour, and a mercenary company will often be outfitted in a moderately uniform fashion, although there will always be the odd lucky individual with a prized favoured weapon (usually loud = good!). Conversely though there will also be units where the prime weapons have been lost or gambled away and hence the slowest and weakest members end up mustering with clubs, muskets or bows.
"Native" orks on frontier worlds will be even more variable - any more advanced weapons will be the spoils of previous battles and raids, with primitive firearms in the hands of the majority.
With Eldar the paradox is in the other direction - they're in decline, in terms of numbers and ambition, but they still have the full capabilities of their civilisation. There are hints in the Rogue Trader rulebook of their mysterious abilities, including mastery of the warp, but in combat they're on a par with, if not somewhat more fragile than, the Legiones Astartes. It seems that any serious encounter between the Imperium and the Eldar should be more akin to Arnie and his team meeting the Predator!
Clearly the Imperium's xenophobia isn't going to accept that they're in any way superior - of course they're decedent - but do recognise that they have abilities bordering on witchcraft. So, to take a leaf from Arthur C. Clarke, I'd suggest that all craft world Eldar (including dreadnought and vehicle pilots) be treated as psykers with the following abilities -
- Telekinesis (level 1)
- Hide (level 1 Elementalist spell)
All abilities should automatically succeed, with no need to test against or track psi-points, but for points value purposes assuming they have 20. Hence your basic Eldar now costs 68 points (without equipment).
These powers are technical rather than psychic in nature though so aren't detectable as such. They're consequently not always available to mercenary Eldar (50% chance) or pirates (25% chance of having these abilities).
I've no idea what these ideas would be like in actual play - in fact I'm sure that in purely commercial terms the direction taken with the rules of effectively having a level(ish) playing field is a more sensible solution. But in my head as big a degree of disparity as possible feels so much more "right".