It would be interesting to see if AI could be used to fill in some of the gaps in the fonts - ie: numbers for his Angstrom font (https://www.dafont.com/angstrom.font)
Someone could also train a model that given some glyphs of a font predicts the rest of the glyphs. Then we can do weird things like give it glyphs from multiple fonts as input to make a hybrid font.
Do you mean relationship in terms of appearance or pronunciation?
Я maps to "ya" sound in Russian, И is "ee" and Н is "N" in Russian and "ee" in modern Greek but in ancient Greek it's something like "e" in "bed" in American English.
Some fonts do not have Cyrillic glyphs. If they could be generated by an adequately trained model based on the other glyphs, then that font's multilingual coverage could expand automatically.