@ Ebon Star
Yes, Line infantry would be the typical wall of lasguns/heavy weapons type army. The vast majority of the IG regiments in fact. Everyone from Cadians to Mordians to Valhallans. A standard vanilla type force. Light infantry are everything from Catachan Jungle Fighters to Elysian Drop Troops. The specialised IG regiments. Your idea, stealth or shrouded for the first turn, could work. The marines have something similar for their scouts.
And yeah, anything to mix up the guard. At the moment all lists are largely the same, and that's a shame.
By the way, what do you think of the Iron Discipline doctrine? Roll 3D6 for fear, morale and pinning tests, discarding the highest, whilst within 12" of an officer or commissar.
@ Sir_Godspeed
That is useful thank you. At least now I know exactly what it is that combat engineers actually do. Making rules for that will be tricky but I'm sure it could be done.
Also, for making doctrines, this might be really cheap but how about 'borrowing' other armies rules under a different name to present doctrines. The Tau's Supporting Fire rule for example? I know that's not very original but if it represents them best then we not? And the idea is, the guard might have the fanciest gear, or be that solid in a fight, but they should be versatile. It's a big Galaxy after all.