However, I cant see how you get around the facts that (1) Austritt dictates severing all ties with institutions that are un-Jewish; (2) An institution is un-Jewish if it is subject to Torah law but does not recognize such law as validly binding on it; (3) The State of Israel, as it is run by and established by Jews is subject to Torah law.
No. You are applying the term with too broad a brush. Hirsch opposed making concessions to the Reform, and insisted on a complete separation from them. I do not find any instance of his (or of his prominent followers) doing the same for Zionists in the Gemeinde. Believe me, if he had intended austritt from Zionism, he would have openly declared it.
It is not for you to declare austritt.
Your sincerity is admirable.