If I was Austrian, I would opt for the civil partnership if the antiquated marriage laws are not updated.
Thankfully, as an American, I don't have to worry about this because marriage in our country is a civil institution, not a religious one 
What do you mean by that ? Here it is both a civil and religious institution, just like in the US.
Marriage in the United States is not popularly understood as a religious ceremony/institution. The vast majority of even conservative religious people in the United States are married in civil ceremonies (with the most notable exception being Roman Catholic marriage rites, which are commonly performed). This is why marriage still remains vastly more popular than cohabitation in the United States even among young, secular couples.
This generally contrasts with much of Europe, where even though most marriages performed there are civil in nature, the historic influence of national churches and state religions on marriage law has resulted in popular perceptions of marriage that are more religious than in the United States.
Granted, my perceptions on this issue are very American-centric and probably gloss over a lot of the nuance contained in modern European concepts of marriage, but I do think the lack of a state religion/national church in the U.S. has done a lot in secularizing marriage here.
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