Unicode Version 11.0.0 will be published sometimes later this year, probably in late June. This is an issue to manage updating Ruby to Unicode 11.0.0. Details to follow.
Just a note, the definition of extended grapheme cluster is changed in Unicode 11 (Unicode® Standard Annex #29
UNICODE TEXT SEGMENTATION revision 33: https://www.unicode.org/reports/tr29/tr29-33.html)
This affects Regexp /\X/ which is hardcoded in node_extended_grapheme_cluster() in regparse.c.
Just a note, the definition of extended grapheme cluster is changed in Unicode 11
This is mentioned at http://www.unicode.org/versions/Unicode11.0.0/, so I was (vaguely) aware of it, but thanks for the reminder. I have created a subissue at #15182. I may have to get back to you for some help, but first I have to fight with #14802 :-(.