I agree with Witham. I think the idea of a chapter of Smith Marines would be awesome, but really, the Smiths are a band that would be nigh-impossible to model a chapter of Space Marines on: they have no trademark look or dress code, and it would be really hard for you to identify, by their looks alone, that they have a connection to the Smiths. Now, bands with a unique look (the White Stripes, Lordi, etc) would work better as Marine chapters: I once saw a CSM army modelled on various personas in heavy metal (Ozzy, Lemmy, Ronny James Dio, etc), and another Fantasy Chaos army modelled on KISS. Those armies work because the opponently immediately recognizes the bands they're modelled on. A band like the Smiths, however, who, while popular, were never instantly recognizable for any trademark looks, will be hard to model and even harder for the opponent to recognize.