So I'd rather see them as a list of options which realms can choose from regardless of government type with the following options:
Dowager King/Queen of Keplerstan
Prince/Princess of Keplerstan
Statesman/Stateswoman of Keplerstan
Eminence of Keplerstan
Royal of Keplerstan
(something religious sounding) of Keplerstan
If we were going to match them specifically to government types then I'd suggest the following:
Monarchy: Dowager King/Queen
Tyranny: Prince/Princess OR Royal (can't decide which)
Theocracy: Eminence
Democracy/Republic: Statesman/Stateswoman
Poll