In SoapUI version 5.5.0, JsonPath library version is 0.9.1. This version was released in 2013. Since, work have been done and the latest version is 2.4.0 (released in 2017).
Would it be possible to update JsonPath library version ? It has be done in ReadyApi and it give user more freedom in assertion. As a reference, you can read jsonpath reference SoapUIPro documentation.