[PhilD]

Interesting house rule, but this will strongly handicap some nations, much more than others, as some have various types of semi-redundant commanders while others don't.

Ulm, for instance, has several Versions of the "commander of Ulm". Are they allowed one of each?

The number of different available mages will also be important (though doing any kind of research will be a major pain, plus you won't have too many battle mages).