You can change your Combat Text font by replacing the font in the addon folder (The name has to be font.ttf)
Note: this addon doesn't work with ElvUI
It is possible to change the font for a critical hit?
Not for the default Blizzard Combat Text no, but you can with addons like MSBT
Any plans on making the addon change the font of the text like miss, parry, enter and leave combat, incomming damage and healing ?
Don't really plan on adding that, but you can change the Scrolling Combat Text for Self font by replacing FRIZQT__.ttf