Will manned vehicles ever follow multi-flyby trajectories?

A while ago, I asked a similar question here, but I think it was confusing, so nobody answered.

Two questions:

• This one is a bit subjective: Do you think that lengthy (+5y) multi-flyby trajectories heading to either Mercury or the outer planets (Galileo, Cassini, MESSENGER, BepiColombo) will ever be considered for spacecraft carrying humans onboard? or will this destinations not be worth pursuing until there are cheaper methods that allow for vastly faster direct trajectories and deceleration upon arrival?

• If yes, then, is it possible for the passengers to board the spacecraft on the last possible Earth flyby, in order to shorten the flight time, or are the orbital parameters inadequate to allow for a Soyuz-ISS kind of rendezvous?

Thank you very much.