A good chunk of those 2/3rds speak English and can wield Latin script (and if not, they should).
Latin script has eaten the world; suggesting Cyrillic for any new language is lunacy.
The number of languages using Cyrillic is vastly smaller than Latin script, and are geographically clustered in areas that belonged to the Soviet Union.
Latin and English script share common ancestry and really are not that different. Likewise people don’t suggest to French and Germans to not use umlauts and accentuation, even though the characters are different.
Latin script has eaten the world; suggesting Cyrillic for any new language is lunacy.
The number of languages using Cyrillic is vastly smaller than Latin script, and are geographically clustered in areas that belonged to the Soviet Union.