PARTIALLY SOLVED
Indeed , GravityForms 2.4+ includes (beta / hidden) repeater feature.
But the class name used in GF is the same GF_Field_Repeater.
I ended up replacing the class name GF_Field_Repeater with GF_Field_Repeater2 in all occurrences in all files of the plugin.
And renaming every occurence of “repeater” with “repeater2” and ‘repeater’ with ‘repeater2’ (note the difference between ‘ and “).
Finally renamed files containing repeater with repeater2 (i.e. class-gf-field-repeater.php becomes class-gf-field-repeater2.php, etc ) and renamed the plugin folder.
Obviously, this is a in quick and dirty mode, still I edited the plugin;
but A/it is no longer supported (Big up and many thanks anyway to the author) so no upgrade available = no upgrade overwrites
B/I guess GF will provide soon a gui for its native repeater.
I repacked the whole working version, so you can download it here
https://www.dropbox.com/s/50kahlyb67gkq18/repeater2-add-on-for-gravity-forms.zip?dl=0
This works at least for me. I’ve just tested it very briefly on a basic form, so I dont guarantee blah blah it will work for you Disclaimer blah blah.