OK - I reckon I’ve got it now - finally !! … (Apols for my slow take-up - In retrospect, it was obvious).
But, let me paraphrase to be sure I’m truly on-the-same-page with you …
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With SP=ON - no change is required to PLv6 bahaviour.
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With SP=OFF - then the following changes are required to PLv6
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Re-instate ability (in preferences) to specify the ICC Profile of one’s monitor
- - as it was with PLv5
– with “Current profile of the display device/monitor” as the default. -
When SP=OFF, the additional Protect Saturated Colors algorithm (that’s currently applied only when SP=ON and also for the Export to Disk process) is applied for the ICC Profile specified in Preferences.
– This ensures the “holy grail” of consistent WYSIWYG
Plus some additional, essential, refinements;
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When using the Compare option, regardless of whether that’s with Geography or without, the same behaviour as above (1. & 2.) must also be applied.
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In the Export to Disk dialogue, the ICC Profile option should default to “Same as Soft Proofing” (rather than “As Shot”) … as another “fail safe” step in protecting unsuspecting users who may have their camera settings = Adobe RGB, without appreciating the unintentional impact).
If that’s what you mean then I’m totally on-board … this would solve all current issues. 
… Thanks for your help in getting this across, Keith … Hopefully, my proposal will now attract many more votes 
John M