As part of 7143984 we added support to launch webstart app using following syntax:

===
var launchParams = {
    "url" : "dynamictree-webstart-no-codebase.jnlp",
    "ignoredparam" : "bb",
    "params" : {"aaa" : "111",
                "ccc" : "",
                "ignoredNonString": 4}};
el.launchApp(launchParams);
===

But it only work for NPAPI java plugin.

We need to support similar syntax for DT plugins too. It is enabling step for 7132539