OpenPLi develop and 9.0 uses subssupport from oe-mirrors repository while the original author is mx3L and he has it's own repo (used in <=8.3 release). The problem is, mx3L is not active in development anymore and he only sometimes accepts pull requests. And there are many forks and private modifications without source code, so there is a lot of mess in available versions. Every version supports "some feature", but there is no "perfect one".
Subssupport just needs new developer who will maintain it and pushes it forward. A similar status applies also to serviceapp and exteplayer3.