I honestly don't see the value in it. Why do I want the possibility of getting fired after competing against my buddies for several seasons and having finally built up a team of my own recruits? Maybe I'm missing something.
The best feature I've heard of so far (or can think of) for OD is the custom conferences that they are actually implementing. That has huge value to me, to allow you to have decent user vs user schedules with teams and a conference of the prestige that you want.
Other than that, the biggest feature I would want for online dynasty would be better web site support. Right now the web site has marginal value at best, if a team has played their game I can see that they played and whether they have recruiting left. But I still can't tell who won (it's wrong half the time), if a team hasn't played a game yet I don't know if it's because they had a bye or what, and I can't even see a team's rank if they haven't played yet. And it does nothing in the offseason. It would be awesome if the web site allowed you to do your recruiting via the web, sim games or advance the week via the web, and in a perfect world it could keep stats too (i.e. you can see your team/player stats/awards for every year you've played).