No, Luke Cage is already confirmed getting a separate 2nd season so Iron Fist should too. The better alternative would be for both to appear in each other's show, like say Danny appears in last 3 episodes of Luke Cage S2 and Luke appears in the first few episodes of Iron Fist S2.

Really, what story is left to tell with Luke Cage? The only major points in Luke Cage's life is his budding friendship and eventual partnership with Danny Rand (which could be season). Following that is with his run from the law again with pregnant wife Jessica Jones due to the accords (another season).

Jessica Jones can only really explore her origins so she has that before ultimately her story completely merges with Luke Cage's.

Daredevil only has one great story left to tell (it dealt with his start. Check. Series 2 dealt with the Hand get in a relationship with Elektra and watch her die. Check). Daredevil's last story should be about Fisk causing his fall from grace and forcing him to become just like him until Matt Murdock can redeem himself, which I suspect will be the plot of Daredevil season 3.

@Innovator said:

I'm hoping they just combine Luke Cage and Iron Fist after the Defenders instead of both having individual series. They really work best together.

Niether character could survive for very long in their own comic book series when they were initially created and, it seems, niether might have much longevity in their own separate TV series... I guess we will see.

Power Man and Iron Fist