Very similar wish - not on Marker Selection Mode but to add some flexibility to Fill Selection Mode:
Improvements to Fill Selection Mode in JMP graphs (combine modes, quicker change of mode, change color/pattern)
☐ cool new feature
☐ could help many users!
☐ removes a „bug“
☑ nice to have
☐ nobody needs it
What inspired this wish list request?
there are different ways to highlight selected data points,
but sometimes, it's hard to see ALL the selected data points (without searching).
What is the improvement you would like to see?
Providing the possibility to activate multiple options at once:
especially: the combination of
- unselected faded
- selected larger
- selected outlined
will provide a nice combination which will make it much easier to see selected data points 
Why is this idea important?
It will facilitate exploratory data analysis in Graph Builder.
more wishes submitted by 
Related wish:
Marker drawing mode: Outlined - individual setting for every legend entry
For each entry in the legend, please add the possibility to specify if outlines are added or not.
At the moment, I can just activate Outlines for all Markers - or deactivate them.
If I want some markes to get outlined, I have to use the Marker Selection mOde and select some markers.
This is OK as a workaround - but I'd prefer a plot which is "stable" - independent of the current row selection.
