What Could Have Been: Celebrated indie songwriter/musician Kevin Gilbert, who had much respect and love for the "classic" Genesis (he performed the entire "Lamb Lies Down" album live on stage), was invited to an audition to replace Phil Collins in 1996. Unfortunately, he (Gilbert, not Collins) had died just a few weeks earlier. There's not telling what a talent like Gilbert could've done to invigorate the band.
Genesis were suggesting writing a concept album based on Antoine De Saint-Exupery's The Little Prince as a follow-up to Selling England. Gabriel opted for an edgier, more Americanized concept album instead (The Lamb).
Casual considerations to replace Steve Hackett as guitarist in 1978 were rumored to include Jeff Beck, Robert Fripp and Steely Dan veteran Elliott Randall. It was later agreed to keep it a three-piece in the studio.
Among the people being considered to replace Phil Collins as lead singer was Fish, who had previously done vocals for some of Tony Banks' solo material. "Generillion" might very well have been really awesome.
Their 2007 Turn It On Again tour started as an attempt to reunite Banks, Collins, Rutherford, Gabriel and Hackett to perform The Lamb Lies Down On Broadway; when Gabriel decided against it, the three-piece band reunited instead.
Attempts were made to make a movie out of The Lamb since the late 1970s, but nothing came to fruition.