Transform XML elements of the same name into JSON properties of the same name

Your JSON example:

object-node {  "value" : "value1",  "value" : "value2"}

isn't really valid: or at any rate, it's best avoided. RFC 7159 says:

When the names within an object are not unique, the behavior of software that receives such an object is unpredictable. Many implementations report the last name/value pair only. Other implementations report an error or fail to parse the object, and some implementations report all of the name/value pairs, including duplicates.

I don't believe that it is possible to embed a FLWOR inside of the object-node() constructor.

You could construct a string and evaluate with xdmp:eval() or xdmp:value():

let $container :=     <container>      <value>value1</value>      <value>value2</value>    </container>return  xdmp:value(   "object-node {" ||      fn:string-join($container/value ! ('"' || local-name() || '": "' || . || '"'), ",") ||    " }"  )

Or build the JSON string and use xdmp:unquote():

let $container :=     <container>      <value>value1</value>      <value>value2</value>    </container>return  xdmp:unquote(   "{" ||      fn:string-join($container/value ! ('"' || local-name() ||'": "' || . || '"'), ",") ||    "}"  )