Hatten:
Not to be that guy, but if you bring the Deathwatch to Black Crusade, that might be missing the point a bit. :P
That was, after all, the joke. ;)
Plucky:
I would like to go for a Navigator, if there was the vacancy for that role - but I wouldn't want to put off any prospective ST with deliniation of what I want over what is possible.
Astartes are hard to write interestingly - larger than life demigod living weapons are bad avatars for first person shooters and challenging even to the best Black Library writers, often they come apart in PbP games.
So anything that trafficks in the comings and goings of mortal humans is awesome. :)
Yes, more realistically, mortal humans would be better. I haven't played in a vibrant RT game on RPOL yet, so if we could figure that out, it'd be awesome. I'd totally be down for DH as well, but RT would be the first thing I'd hope to see. I could fill in wherever.