Hi,
We're hearing you. We actually want to completely redevelop the mass action system in order to be more flexible, more consistent, etc in the future.
That's however a really big development as there are over 10 000 lines of code to handle the mass actions system.
It's a project that's going to take months when we start it.
On our end, our schedule is full for the next few months, which means we won't be able to finish such project in less than 6 months if we decided to go for it now.
That's for these different reasons we don't want to develop some custom plugin for the current system for your specific needs.
And as I said, cost-wise I don't think it would change much if you did your own custom script. You could totally make it into a plugin and have options for it, if that's necessary.