You can already do the sub FSM using the "run fsm" action with templates using exposed variables as inputs.
Really powerfull once you get it. Don't be like me and give up trying "run fsm template": it's basically the same without the inputs and I'm not sure why it is still around.
The only thing missing is output variables: currently, you need to use "get host infos" to get the host and its FSM name so you can use a "set FSM
variable type" on it. It's a bit tedious because you have to make sure your variable are named correctly and not mix up their types. It would be awesome to have a little checkbox to click so the host FSM would automatically retrieve needed variables from the sub FSM.
I was rooting for the group FSM as much as you few days ago and now understand why the request is ignored, the idea totally double with the "run FSM" action.
Still, a simple group tool would be welcome: being able to draw a rectangle to organize things. Also being able to add icons on states would be welcome. These are just visual but help maintaining things clear and effective for future you who is going to open the hood one day.