Hah, you know I've become so used to the ADS I must admit I stopped looking for planets via parallax, but you're totally right. I'm sure they said something about things being there and not being detectable with regular scanners in 1.4, so it's probably worth looking.
During beta, somewhere near the new UA hot-zone, I actually followed a medical convoy out to a undetected planet (I think Ratking15 also found something like this near Soontil), it didn't actually resolve to a full planet in SC, but you could just about make out a fuzzy white blob/dot during the approach.
I'm 90% sure I had already ADS pinged the whole system when I arrived, so it wasn't part of the main system bodies, and probably just there for the convoy when they dropped out of SC.
When I got there (i.e. dropped into the convoy's wake instance) it looked like this:
Anyway, could be worth seeing if we can find a hidden system body like this, but I wonder if it might have shown up already with operation scour going on.
Maybe the ring around Merope 4 is where 4A used to be..? *dramatic pause*