I'm in complete agreement here. It might lead to dropped games, but honestly dropped games happen anyway. I think I've only completed two games where at least one player hasn't dropped, and one of those was a two-player game.
And honestly, it might prevent dropped games. People drop games when someone else is taking a really long time and then they forget about it or lose interest. If it gave us the option for 5 minute (or even 3 minute?) turns, it would deter people from joining who don't want to play until the end, thus making it easier to complete a game without a drop.
I'm curious to know what percentage of 3+ player games are played to completion without any drops.