Please don't ever make the mistake of confusing "shall" and "will".

If I want to paraphrase the sentences, then "this too will pass" is a simple prediction. This is simply your idea. "This too shall pass" has more nuance. It means that you expect the situation to pass, out of necessity or obligation.

¨This too shall pass¨ is an idiom.  ¨This too will pass¨ is not an idiom. Because in modern speech we do not often use shall, I suspect that some people may occasionally misquote the idiom. 

To verify if I am correct about this, I put both phrases into Google as the search term.  If you can search Google where you are, you will see that even if you use this too will pass as the search term, the whole first page of results come up for ¨this too shall pass.¨