iPhone iMessage retention

It seems that retention policies for iMessage on an iPhone are too limited. I strongly recommend allowing more granular management of that. For example, there are some threads of group texts with family that I would want to keep forever. But I have a thread of commuting alerts where messages older than 3 months can be deleted. There are other threads that would fall in between those two. So THIS is the type of flexibility we need in managing our devices. Please make this happen, Apple. Thanks in advance.