Unfortunately, it is not possible to use s_class directly as an initialization for a Simulink bus signal.
Bus signals in Simulink require elements to be defined as structures. While s_class is a class definition in MATLAB and a class object instantiated from s_class would not be directly compatible with Simulink busses.
You will need to convert the instance/object of s_class into a struct to use it as an initial value for a bus signal.
One way to achieve this is by defining a method in your s_class that returns an equivalent struct object.
For example, you could add the following method to your s_class definition:
function s = asStruct(obj)
Then, you could initialize the bus signal like this:
busInitVal = s_obj.asStruct;
The busInitVal struct can then be used as the initial value of the bus signal in Simulink.