I understand your point that updating large scripts to do the same as before is nothing to be happy about.
But anyway, I think this issue is more related to JSONPath than SoapUI 5.7.0 as other JSONPath implementations produce the same result as 5.7.0.
During the past years multiple JSONPath implementations emerged and evolved (Goessner, Nebhale, Jayway to name few), the website https://jsonpath.herokuapp.com/ provides a nice comparisson.
My conclusion is to use the safest possible JSONPath (works in multiple implementations). Then there's high probability it will work in different times and places.
Similarly, also other REST API technologies lack standardisation and the tools still aren't as mature as their counterparts in WSDL/SOAP/XML stack.
Regarding the bulk updates of SoapUI projects -- editing project xml (either by scripts or by smart text editor) is the most efficient method for me, even hundreds of changes can be done quite quickly.