My first husband and I (have two girls together - now grown) had the "black and white" arrangement - he rarely fulfilled his 1/2, and I was always the one who picked up the pieces. Nothing else would have worked for us.
My 2nd husband and I (we have 1 girl together) had a very "casual" arrangement and it sounds much like the arrangement that you have now. We often did things together or picked up where the other person left off. However, we did have a "black and white" written arrangement in our divorce. That was very helpful when we were not able to see eye to eye for periods of time after our divorce (we divorced when our daughter was an infant and she turned 18 this year so there were times over nearly 18 years that we simply were not getting along).
People would comment on how closely my 2nd husband and I co-parented our daughter and how lucky we were and our daughter was. However, there were "downsides" to this type of parenting that have to be considered. My 2nd husband really loves his daughter, but often the "true responsibility" of raising her came down to me. I'm not complaining, but not only was I my daughter's safety net, I was often his, too. Instead of ever calling on his family to help when there was an issue, I was expected to take care of it. If finances were tough, he was the one who always left me holding the bag. If I had it to do over again, I would have gotten my 2nd husband to take a little more responsibility regarding the raising of our daughter - he never really learned that just loving her wasn't enough to raise a child. Love is important, but so is food, clothing, being on time, homework, etc.
You mentioned that you are not in a hurry to finalize your divorce. I think that you are making a mistake in that regard. Get the formalities out of the way. Get everything in writing. Divide the money, responsibilities, etc. now. If you guys can get along and do extra for the kids beyond that, that is great. However, have something written in stone now can really save heartache later.
Finally, the other real barrier for parents who are separated yet co-parent as much as I did (and you are now doing) is getting into another relationship. I know it is way too soon for that right now, but finding a guy who is willing to go along with this unique style of parenting might be difficult. I was really lucky - my husband and my 2nd husband get along pretty good, and my husband rarely had a problem with how we parented. However, this may be because my husband didn't bring any children to our marriage (we have 3 boys we adopted together) and didn't have an ex of his own to deal with.
Good luck!