As one of the maintainers of the containers package these are the kind of issues I have to consider*.
I share these concerns too with Johan, especially about code duplication and package maintenance.
Kudos to him for stewarding it so successfully all along for I and countless others appreciate his work. And I think it's unfair to push work around like this. What happens is open source fatigue and you find your best contributors leaving.
Traditionally, if you found some missing function, you would roll your own package and upload it for the benefit of everyone.
The proper resolution of this proposal is Data.MissingSeq.filterM.