What rock groups could have overshadowed Disco in the mid-late 70's and pushed it out of the limelight?
I was watching Behind the Music about Grand Funk Railroad, and someone said that they should have kept going after 1976 and killed disco. What other rock groups could have overshadowed it?
Some thoughts.
This is a bit of an apples and oranges question.
First, look at the demographics. Disco arose from the American R & B market, the Northern soul demographics in the UK, gay and urban culture, European club culture, and the like. Above all, it was dance music. The core groups buying this music are not buying all that much Led Zep, Grand Funk, or Emerson Lake & Palaver. For a music to replace to disco, it would have to fill the role disco filled and heavy metal, prog, or stadium rock do not do it. The music would have to be club music and urban. Punk and "new wave" (a term allegedly used by Sire Records' marketing people to avoid the stigma of the punk label) sorta aimed at dance music but really was focused at different purpose than Disco.
Prior to disco many who would be in the disco demographic are buying other forms of urban dance music--from artists such as Smokey Robinson, Arthur Conley, Aretha Franklin, The Temptations, etc. R & B music of the Motown variety and the grittier Stax/Atlantic was huge in Europe and in the states--and very influential. Later, the Philadephia sound came is even more dance oriented. You have these American sound copied by UK based groups such as Hot Chocolate and David Bowie. Indeed, Bowie's Young Americans is a homage to the Philly soul sound, which he combined with his glam-rock. Young Americans has a number of danceable songs, some of which receive play on radio in stations featuring predominantly "urban" (black) music, including the proto-disco hit Fame, with an obscure Anglo-Irishman by the name of John Lennon on backing vocals.
Punk culture, like disco, placed a heavy emphasis on dancing. This is like the roots of rock, as early rock was dance music. However, punk dancing, unlike disco, was not what would be considered romantic dancing. Rather, punk pogo dancing and the like were more an involvement of the individual involved actively in the musical event. Still, is considerably different that say reverentially passively being be at the event as a mere audience member.
Record labels such as Stiff Records mocked the reverence of "Art Rock," as prog rock was then often called. Stiff sold t-shirts that were emblazoned, "Fuck Art, Let's Dance." (Another indie label, in turned mocked Stiff, with a t-shirt emblazoned, "Let Art Dance, Let's Fuck.") Stiff offered what might be termed power pop today, with artists such E. Costello, Nick Lowe, and the Yachts, as well as the punks The Damned. Some of this could be dance music. So to supercede disco, I think you would have needed something danceable and acceptable to Disco's core audience.
Groups that attempted to provide this included any number of "new wave" groups such as The Talking Heads, who had a big club hit with their cover of Take Me To The River, the B-52s, Blondie, and the previously mentioned David Bowie. This, of course, is a very white bunch of folks. The appeal of such music was probably rather limited to an important demographic segment of the disco market--African-Americans, who tended to favor more culturally relevant music. The African-American R & B greats often easily transitioned to disco type material. Marvin Gaye, for example had a big hit with Got to Give Up.
So for a music to replace disco, you would need something that appeals to its demographic, and neither Prog Rock nor metal are it. These are primarily white, suburban music. Possibly reggae/ska would fill the role, as it is danceable and might have had some appeal across racial lines.
(And don't even begin to consider the role of Krautrock & Kraftwerk on this mess.)