Sadly the timescale you are speaking about is too long. Both Manchin’s and Sinema’s terms end in 2025, so primary challenges are not going to help Biden with his agenda this term.
I thought that the Democrats should have publicly pitched the 1/6 Commission as the litmus test: Manchin either needs to get 10 GOP Senators or change his position on the filibuster. Now that he has started, he seems to want to move the goalposts each time the GOP blocks a piece of Biden’s agenda.
Manchin’s substitution of the Lewis Act for S.1 makes me think he entertains the notion that he can get GOP support for it, and, since I am more cynical than the average bear, I worry that he and Mitch will pass a watered down version of the act to prove that bipartisanship can work, and take the pressure off Manchin to kill the filibuster.