Cyrillic in your fonts is great, however these days most of Cyrillic fonts contain glyphs for letters used in Russian before the revolution of 1917 (and the consequent orthographic reform of 1918), namely
U+0462 Cyrillic capital letter yat
U+0463 Cyrillic small letter yat
U+0472 Cyrillic capital letter fita
U+0473 Cyrillic small letter fita
U+0474 Cyrillic capital letter izhitsa
U+0475 Cyrillic small letter izhitsa

As of now there is only fita (despite the most frequent of these letters was yat).

Bulgarians would also ask for big yus (U+046A — capital, U+046B — small), used in Bulgarian until 1945.

Having all the four letters would be really good for using your fonts in the humanities.