I used to get along with my son's exstepmother...after about a year we started talking and got along just fine. Then she left my ex and he replaced her with a monster...

So, peace happened...it was brief but it happened.

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We don't see things as they are, we see them as we are. ~Anaïs Nin

I think it's possible, but the exception that proves the rule. If a relationship ended truly by mutual decision so there's no lingering feelings, with the bio-parents seeing themselves as equals & true co-parents, money not being an issue for either party with regular agreed CS paid, and stepparents coming into the dynamic welcomed and given support, then sure, it can happen!

"God never gives us more than we can cope with, I just wish he didn't have such faith in me!"

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"There are two things over which you have complete dominion, authority, and control over - your mind and your mouth".

I think there's always going to be a conflict of interest making it very difficult to maintain. Not that it's not impossible, but it's not likely either, IMO. You have two groups involving some of the same people who will make decisions based on the best interest of their home and themselves...and sometimes that conflicts with the other home/group, causing conflict. And the majority of the time, the SM is guilty by association.
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"Most couples have not had hundreds of arguments, they've had the same argument hundreds of times."

I used to get along with BM. She tried to start a bunch of stuff with me on 2 occassions so now I don't deal with her at all.

"If I turn into another, Dig me up from under what is covering the better part of me" -Incubus

I did for the last five years until the last month. BM is now taking to telling the kids to lie and keep secrets from their father. I have always stayed out of communication and finally when my child got dragged into the mess, I sent a letter. Now it looks like we have to go to court to settle custody issues that worked fine the last five years. I just can't figure out where it all changed, except to say she got married in November.

It is possible to have a good relationship and we did for five years. But, now they are so far apart on raising teenagers that the drama has escalated to being so ugly.

Getting on with BM is rare. It only seems to coincide with when DH bows to her every whim and she feels like she's completely in control, even when she knows she's completely taking the piss. Now DH doesn't dance to her tune anymore, things are as bad as they were in the beginning.