Yeah I'm stuck at an implementation roadblock with MSC-21. In the meantime I'm working on changing XML parsing to create updates instead of creating the models, which is enough to divert the issue for a while...
In principle, MSC-21 will allow us to install services in any order without batches, and they'll start up as soon as their dependencies are all resolved. However there's a big gray area around optional dependencies. I won't hijack this thread with that discussion though.