uh, . . . actually space marines do that. they dont scavenge like orks do, but they still take weapons from fallen enemies. . .

Well here's this.
Space Marines call out for Servitors to salvage a battlefield...
Orks call out the Gretchkins or other orks to salvage a battlefield...

I'm thinking along the lines of SW's MMORPG. However...
Gathering : Have a skill on CD or something of the sort and have'em salvage a battlefield, the more players there are, the higher chance of gathering materials yet the less chance of the salvage being successful. If you get the idea. Or perhaps they have to secure / defend an area until the gathering's complete (A bit like Firefall).

Crafting : Whatever gathered the scraps and what not from a battle, goes to your HQ. From there, you can see everything which was salvaged and work from there, what to do, how to do and all that jazz. Possible upgrades for the Forge you're using or the Industry you're using, different localities "control" would perhaps ensure a higher success rate of shipping materials you may need to finish upgrading a weapon or building a weapon, or armor, or melee weaponry.

If there is PVP, it would be interesting to have Guilds / Legions / Whatchamacallit Forges, where the stuff is gathered at and worked, perhaps even an upgrade to the Forgeworks and whatnot.

The idea is a brief summary of how it'd work.
I actually have an idea of how it could be processed in an interesting way.

as long as what I get crafted is super cool and not mega lame I would not mind it.

Tottaly Agree with you Man!

After all... the Salamanders blacksmith the crap out of their weapons.

My crafting gamer soul want it, but the reality says that no, nope

If there is any crafting system, probably will be more like some sort of personalization system not the crafting that almost all of us are thinking.

For Orks this would work perfectly, mainly because 99% of everything they own or have is built from the ruins of one thing or another.

For the other races it would require to upgrade certain things IE ( think wow enchantments ):

Space Marines - They could take the armor from a kill like metal and craft a extra spike with more damage or something.

Chaos - draining the blood of ones victim to infuse certain attacks or a chance on hit or something. Nothing ground breaking but something to give a little extra play to.

That would be my vision for crafting but I would also like to see cosmetic stuff like TF2

I believe it's been established there will not be any farming for materials from collection nodes in this game, (e.g. Mining mounds, herb spawners, etc) which require a player to move about the world using a pick axe to mine or a shovel to gather herbs, this game is about there being only war. I believe the developers mentioned this in an interview or somewhere early on.

I find the idea of a Space Marine taking a brake to pick flowers for any purpose other than to stick it in their hair to be lore shattering for me, not because of the little things, but because of the most important thing, the knowledge of technology in Warhammer 40 000 is held by and understood by those who are fully trained in it's knowledge for most races and in the Imperium only the Mechanicus or authorized persons by the Mechanicus know how to construct technology. And the same can be said for other fields of knowledge. Most Orks outside meks don't know how to put together anything they use and if what they use brakes they just buy something with teef to replace it or steal it from someone else. Eldar spend their whole lives focusing on perfecting themselves at one aspect of martial art. The only faction in the game currently where knowledge isn't restricted is Chaos, but individuals who follow chaos tend to be mostly concerned about whatever their obsessed with and simply couldn't be bothered to put their knowledge to use other than to meet their own ambitions, which for most is trying to please the dark gods so they can get what they most desire.

I hope there are rare things to craft, I have always wanted to see rare receipes that can be dropped but can be only crafted once per scroll. To make another you must wait for another drop makes them rarer and less material reliant and fits the rarity.

I would love it if Sorcerer could try craft daemon weapons. The weapons would be very powerful like you expect, but one mistake and next thing you know your half way down the gullet of a bloodthrister. The greater the daemon the better the weapon, but also higher risk.