What will happen if an Iranian national applies for EB-5 during the ban?

Based on the available information, there is no plan to permanently ban Iranians. The plan is a temporary suspension. However, in order to protect your interest, you should have an option in your EB-5 agreement that would guarantee the return of your fund if it is not politically feasible to process your petition. Advisably, consult an attorney to ensure all your interests are protected before you sign any agreement.

There is nothing to bar an Iranian national from filing an EB-5 investor petition on Form I-526. Although the ban has been temporarily set aside, at worst it could delay the adjudication of same.

Hard to tell, but you should negotiate with the regional center to get your investment back if you are not able to travel to the United States; attorney fees will be gone, as the work was done.

There will not be a permanent ban.

The right to sue depends on the terms of the subscription agreement. Many projects and some banks will not accept Iranian investors. It appears unlikely Iranian investors will be permanently barred from immigrating to the United States. However, you can raise this issue with the regional center and maybe amend your subscription agreement to fit your specific case.

There is no prohibition on filing the application. Being issued a visa is an issue temporarily. You should assume you will not get your money back no matter what.

So much is uncertain that, as of now, even though the courts have issued a temporary restraining order halting the implementation of the Executive Order restricting travel/immigration of the nationals of the seven countries (including Iran), I would advise to wait until there is a clearer understanding and implementation of what DHS/USCIS policy will be before beginning the EB-5 process unfortunately if you are a national of one of the seven countries named in the Executive Order.