Technicality: pcsx2 is already 1.7 in Batocera. Batocera just uses the older wxwidgets menu interface instead of the QT 5 interface. The retroachievements was only made to work on the QT 5 interface and wasn’t backported to the wxwidgets.
With that said, retroachievements itself needs to be intergrated into Batocera to function properly within ES. That’s something that takes additional time to do.