This might help you without a new feature.
It uses the example that @mathieubossaert posted here, extending the KML/geojson export from @Xiphware & @detrygeoffroy.
I put the geopoint inside a repeat to allow selection of 1 to many points, these then get converted to WKT as POINT / POINT Z strings inside the repeat and finally rolled up into a MULTIPOINT () / MULTIPOINT Z string outside the repeat.
Being inside a repeat, you can also add additional questions related to each point there as needed.
multipoint_example.xlsx (19.7 KB)