Unless I have misunderstood your request, this is already possible in Studio One.
You can set the time signature in the transport bar:
When set to 11/8, you can see as an example that that one measure highlighted here is in 11/8 time:
You can also click on the timeline and add any time signature at a point in the timeline so that you can have a song with changing/multiple time signatures:
If you are editing a pattern for 11/8 time, change the steps to 11 and the resolution to 1/8: