Lexicanum will answer you, Books will answer you, go ask Graham Mc Neil why IG are the weakier race of he game, it's just Human ! like you and me with laser gun ! nothing more. It's not super soldier ! for me a guardsmen is skilled like a gaunt nothing more. For me and for the Lore

Imagine you in this world, you think with a little pewgun you can killed that monster who are orks ? Fight against giant Astartes ? try to kill speedy Eldars with deadly danse of death ? Or fight against demons ?
I think a human is a meat in this world not more

The Razorback's heavy bolter still can't glance the Chimera's AV12, and it's still AV11. Chimera still eats it for breakfast even with just a multilaser. It would have to spend 20 points on the lascannon upgrade to even stand a chance, and the Chimera can get an autocannon for half that.

And when you're talking about the Imperial Guard, you really, truly do not want to drag all the vehicles into the equation. Trust me, I'm being generous by only considering dedicated transports.

Really, if the Imperial Guard was as weak as some people seem to think they are they would be complete pushovers in Tabletop and DoW. They just require that you invest a little more in their equipment (which you can because they're cheap) and put a little more thought into deployment and positioning than Space Marine players are used to.

I want the Imperial guard in this game simply because I do not want the Imperium represented by only the Space Marines (the group I fear is going to be filled with 12 year olds). IMO people who would choose to play the guard are going to be more tactically sound and more dedicated to team work than the supersoldiers handed out like candy to anyone who even looks at WH 40k.

Unsurprisingly, I would love to see IG in this game, I do appreciate that this will take a long time to implement if it is at all.

Looking at what you have said across this thread (not read all the other ones yet sorry) I think it would not really be that much of a stretch to get the IG into the fight, but as I know has been said already they would have to fight differently than SM, IG would have to have a cover mechanic or as was suggested earlier be a "squad" like the Gibbering's from Allods as IG are to squishy to fight SM on open ground.
But that's really going to have to wait till the game is released before we can see.
And just to get my bit in on the rest of the things Raised in this thread:

I do agree that a guardsman out of cover hit by a bolter shell is probably going to die, went back and read how they work and, unless its out side of the max range or under the arming threshold then he's dead (baring misfire ect)

I understand that the Eldar armour is self reinforcing at point of impact but because it is a mesh that is applied in layers its effectiveness is limited, where as it is stronger than flak its a bit weaker than carapace on average ( I will double check this though as its been a time since I looked it up.) the wraith bone armour are much more affective but less common.

Lasguns, honestly with these there are tones of them and its hard to work out how effective they are, and I appreciate its a bit of a copout to talk about just changing the variable settings on them, but from what I have read in the (admittedly Guard centric) Dan Abnett Gaunts ghosts series they are able to kill SM on joint and eye shots.

Sorry for the long post, just been reading for some time and wanted to get what I was thinking out

Here, i'm agree, a little squad with 2 NPC who follow you, here it's ok, 3 guard vs 1 marine can be more logical, but the only problem is again wich side they take. Look, for Dk you have a entire explanation because of the fight between guard and BR , in Soulstorm more simply, they completely forget the lore and now soulstorm is => Boreale is dead, SoB and IG have disapear ...
We can't introduce 4 régiments who are heretics, people are'nt be happy if they don't see Cadian or something else and you can't decide Marines are Heretic, 4 primogenitor Chapter with the more Proud, Ultramarines ...

I really disagree. It has nothing to do with Lore and is simply about materials and physics...

Exhibit A. Flak Armour: It is meant to provide defense against low-velocity, dispersed damage, such as explosions, shrapnel and ricochet material, rather than to protect against a direct impact, in which case the armour's protection is almost negligible.

Exhibit B. Bolter Round: A .75 caliber weapon, the Boltgun fires a self-propelled explosive 'bolt' which explodes with devastating effect once it has penetrated its target, effectively blowing it apart from the inside.

A .50 caliber round hits in at 12.7 mm and even normal rounds fired from that gun are devastating. That round alone would break ribs from the force alone, and all that is saying the armor stops it. However the Bolter fires a .75 caliber rounds measuring in at 19.05mm in diameter. That is literally .75 inches across. You are telling me that a lightweight armor that is made for normal troops is going to stop a round that is .75 inches in diameter and is made to penetrate and explode? I am sorry but I simply don't see it happening.

Well, just make it so story-wise they're on the same side, but gameplay-wise they juts happen to start far away from each other (and thus are unlikely to share a border) and have contradictory objectives (thus requiring strategic backstabbing).

So they would sort of be on the same side, but still fighting when their interests contradict each other.

If we could vote IG in instead of another Space Marine chapter, I wouldn't mind. I'd love to get me some Raven Guard action but IG would be cool.

Now the problem is population ! ^^ if you give Imperial and Spaces Marines we will be over populated ( Marines a already over-populated if you give them Imperial too... )
But this is the only solution yes, but you give more tanks, more soldiers for the Imperium than the other faction ^^'