The "non-Plus" version has always had access to expedited lines (at least I can at EWR).
I just ran the updated "Mobile Passport" app on my iPhone. I was given the option to upgrade to Plus, which I declined. I was then given the option to DELETE my data (passport info I already have stored in the app), or upgrade to Plus to preserve the data (one of the features of Plus is to store encrypted passport info, which I already have stored from the earlier non-Plus version).
It seems that if you don't sign up for Plus, you'll be forced to manually enter your passport/etc details on arrival on every trip. I say it "seems", since it's difficult to find any real info so far.
Also (from their FAQ page), the non-Plus version of the app includes ads, where the Plus version does not. I don't remember if the old version of the app included ads before (I don't remember them, but maybe didn't notice)