it depends on the type of league there is going. Weariness will set in if one player runs away with the league yes but if it's a season long fight for the top I think interest will be quite high as rivalries will already be in place for the next season. Nothing sparks the interest like knowing you have 5-10 games on the roster that truly matter(and yes I know the bot flush people will quote the heck out of that).

Promoting in second would do a lot of good for the people who finish second but for those who fought it out and lost to the 3-4 good teams in the series and ended up in fifth, demoting would be demoralizing. I think we'd have just as much attrition due to that.