Hello Mel,
There has never actually been an 'all perspectives' voicing parameter as such for the hi/low EQ -- prior to v5 the four output simply perspectives didn't exist, so the (only) low/hi EQ voicing parameter was for the only perspective, which was effectively output perspective 1.
The reason that there can't also be 'all perspectives' adjustments for a few voicing parameters (including the lo/hi EQ, and release truncation parameters) is that, unlike other adjustments, they are 'absolute'; they cannot add together with other adjustments. In the case of the lo/hi EQ that's because there is only one real-time voicing EQ filter per pipe per output perspective. Hence if there were also to be an 'all perspectives' lo/hi EQ adjustments and you specified a differently shaped filter (e.g. a +5 dB shelf at 12 kH with a broad transition) from one of the individual perspectives (e.g. a -3 dB shelf at 1 kHz with a steep transition), then there would be a conflict, because either the 'all perspectives' filter could apply or the per-perspective EQ, but not both (since both would require two real-time filters). Whilst one could conceive of an 'all perspectives' lo/hi EQ adjustment that, if non-zero simply overrode all four of the perspective lo/hi EQ adjustments, I think people would find that confusing.