i have a very strong feeling that in the 40k universe the kroot has a bigger part to play.
i can see a gap for a low toughness, minimum save army that infiltrates, can shoot well, do ok in Hand to Hand. forge world offer some cool kroot options but there is room for more. HQ's could be some sort of clan chieftain, ELITES could be snipers, head hunters, TROOPS could be the normal kroot but maybe some other options to add flavour. cavalry (riders) beasts, FAST ATTACK could be riding large lizards, you know the kind of thing.
i see kroot a bit like the ratskin scouts in Necromunda. started off a few additional models to beef up your gang then ended a gang in their own right.
im SURE kroot could be a major option in 40k, what do you all think... if you even care?
They did have a full army list in 3rd or 4th ed, was a chapter approved list but still seemed to work quite well. I think that was before the FW extra units so with those as well you'd probably get a fairly well-rounded army. The Kroot are pretty technologically inept though so you're really going to struggle against tanks, as they have no equivalent so far and no heavy weapons.
There's always room in the 40k universe for more races, typically you get an extra one each edition, though 5th hasn't had a new army yet. 2nd edition had the most new armies released for it I believe, even if you don't count different marine codexes as new armies.
Personally I'd love GW to do something interesting with some of the races already hinted to, like the Kroot or the Demiurg. They definately need to do something new rather than repeatedly re-re-re-re-releasing the same space marines and then saying they're the only thing that sells. Of course they are they're all that you release.
There's plenty of stuff in the background that GW is just plain ignoring that would make great tabletop armies, how awesome would for instance an Adeptus Mechanicus army be? They do have full armies, they're in the background all the time, and there would be chances to have a lot of compatability with the IG plastics to boost the variety there. However doing something 'new' is probably seen as too risky by the shareholders so we'll just get more and more of the same space marine chapters.