In SpartaNova, there is a flat base income tax rate of 70%. For each year of military service that a (potential) citizen performs, his or her future tax rate is decreased by 10% if the service occurs during peace time and by 15% during wartime if in a non-combat role, and 25% during wartime if in active front-line combat, down to a minimum tax rate of 20%. There is a special exception for special service fighters (i.e. seal teams, and other dangerous jobs like bomb disposal teams), nuclear submariners, air force pilots and higher-level intelligence workers all of which receive an additional cut of up to 5% per year of service, down to a minimum of 10%.
Service is voluntary and standard expected service is 2 years, but a serviceman can elect to serve longer if he or she so desires and is not otherwise blacklisted from the service for some reason. Veterans (a la Heinlein's Starship troopers) also receive the full right to vote (non-veteran residents only vote in local elections). There is no "family" tax rate, and the income of each spouse is taxed according to her service or lack thereof, and dependents lose their tax-dependent shield at age 17, when full 70% income tax (or military service) kicks in.
It follows that most rich people would be strongly incentivized to send their children to serve in the military to diminish their future tax burden. Poor people would have the same incentive, true, but the rich would have a disproportionate amount to gain from diminishing their flat rate.
Would a society where the sons and daughters of the richest all serve (if able) be significantly different from ours? For instance, would the nation be much more careful about declaring war or engaging in what we euphemistically call "kinetic operations"? Do more important implications of this come to mind? Yes, I am aware it would likely be an even more unequal society, but I have never mentioned what the taxes are being spent on, or what the inheritance tax rate is, so perhaps we should remain agnostic on that a little longer.