They might, or they might not.
If you look at the One X +, the only feature present on that device over the One X is 64gb of ram.
Lets say that they Make a One + - what could they do? Bump it to a Snapdragon 800? Sure that would be impressive, however the jump from 600 to 800 is about a 35% boost, whereas from S4pro to 600 its a 40% bump.
So, is that extra 35% really worth it, when you can wait another few months and get their latest flagship which will probably be a 70% increase over 600?
As far as I'm concerned, rather then waiting for "+" versions, it is wiser to purchase initial releases.
I think you have a typo there 64gb RAM then you got a deal! Also 800 snapdragon not only boosts the performance by 40% it also has a better GPU, better architecture, better power management, implemented ad on WIFI so it's now a/ac/ad/b/g/n and has LTE technology which has a maximum of 150mbit speed.