I am just worrisome against even a small mass limiting of voter rights because of what it can grow into.
This also has problems with it basically being a mandatory form of draft to supply voting rights, which does mean that it isn't mandatory though. But since I consider voting is a right, there shouldn't be any artificial barrier for an adult to obtain it.
Also, this system odviously gives prefference to richer individuals, because I am assuming that the 2 years of work will have low wages, or it simply provides for living expences while you are working.
If some rich person doesn't need the money while they work for 2 years to go to college later, then your system isn't fair to people with a lower income. I am sure a system would develope when only the more wealthy can vote, even if there is as motivated and self sacrificing poor.