Have dived into Capella meta model. Below are some findings that helps to integrate BTree and FncBlocks with it.
There is three types of Behaviour elements
StateMachine, Scenario are generally used.
BehaviourTree should also inherited from AbstractBehaviour.
AbstractActivity is very close to SysML activity. They can include activity nodes, pins, control and object flow, partitions and so on.
It’s possible to use this meta model but not introduce a new one for FuncBlocks.
All Capella functions are inherited from ActivityNode and as a result can be used as part of activities.
All Capella functions can call other Behaviours. They have a reference to called AbstractBehaviour.
FunctionSpecification can be linked to every Capella function and used to specify behaviour of function using activity.
General conclusion from this finding that the need to specify behaviour of atomic functions using some activity diagram is not new. It’s not implemented in Capella UI and is not used in Arcadia. But activity meta model is an integral part of Capella meta model and can be used while extending Capella for behaviour specification of atomic functions.