I don't know whether being more common in the past than now makes a name dated or not, tbh. It's certainly gone from top 5 when I was born in the 80s to well outside the top 150. But I still think it's quite timeless. It will never be an unknown name.
I teach two (one age 10 and one age 11).
But when I was growing up we frequently to label ourselves Rebecca, Becca, Becky and Bex plus sonetimes use surname initials to avoid confusion. We were everywhere.
I like my name but I don't like it shortened (I'm ok with Bex at a push). I have come across Rivkah as a nickname but I think that might be more a variant than a shortening. Really like it though.
I always wanted to be spelled Rebekah. Looks nicer, is the original Biblical spelling and makes the name a bit different.