My immediate gut instinct says Grimes to the PS.
I don't see Kubiak doing away with precedent, and the precedent has been that the Texans carry 3 RBs. Well, that might not be true. I seem to remember back in the Ahman Green or Ron Dayne era here that we ended up having only two RBs on a game day roster for some reason, and they both got dinged up and one of them is out there hobbling around because there was nobody else left to pull RB duty.
Maybe I'm wrong though. I know that one time last year, Foster was banged up and Ward got banged up (a blow to the head or something), and I think Ben Tate or Chris O. ended up being the only RB we had for the rest of a game. IIRC.
But I don't see us carrying more than 3 RBs, and IIRC the only guy out of the four RBs who is PS eligible is Grimes. And frankly, teams tend to not poach other teams' 53-man cutdown guys...so a guy like Grimes (who is raw in terms of NFL experience, just like other teams' version of Grimes right now) will likely pass waivers and hit our PS squad where he can be called up if any of our starting three RBs get banged up on a Sunday in the reg season.
I think Case Keenum, if he has a decent preseason and looks like Chase Daniel did for the Saints a few years back, will be poached off waivers if we try to get Case to the PS. But Grimes? I think he is a PS guy all the way, IMO.