Perhaps, but there's still one big problem with this suggestion, on top of the whole "the army can overthrow the government" thing. The Romans did not see their state as being a collection of equal territories, as the Americans largely did. They saw Italia, and even more so they saw Roma, and they saw the rest of the Empire. To them, Rome was everything and the Empire was spoils of war. There weren't that many citizen-class people in the provinces, and those who were officially citizens were partly what the fledgling USA would call "landed gentry" and a large part (maybe 80-90%?) men who had served their 25 years to be given citizenship. Those veterans had little interest in voting, they just wanted the benefits to standards of living, but can you imagine the result of those men voting anyway? Imagine if in the present day you accumulated all the eastern seaboard states together in the electoral college as one controlling state, and then gave the rest of the states to the US military to control the voting of. These "voters" are from virtually the same background, with virtually the same life histories, have signed up early as military recruits and all been given virtually the same farming life after they had retired. They're probably only going to exert political will in one of two ways: a militaristic fashion favouring giving soldiers more power (and money), or towards potential legislation which allows them to retire in peace and not be constantly disturbed or taxed by the state. And if you give them too much power, that's going to wreck Roman politics.
Of course, this talk is diverting me off my original course. The citizen base was too small outside of Italy, and even those in Italy viewed Rome as the be-all-and-end-all of politics. You're going to have something like 95% of the Roman "Assembly" being heavily pro-Roman and they are going to react angrily to the provinces having any say - indeed, they will be furious at the provinces even having the right to have a say - in politics, and their legislation will probably be very racist and aimed at alienating the rest of the Empire in a "shut up and do what we tell you to" kind of way. Really you simply cannot give power out to the whole of the Empire like this.
But really, Don Georgio is right. You have to think like a Roman, not an American. Could the Roman Republic/Empire work on the 1775 US model? Heck no it couldn't. There's no way this could work by simply implementing a constitution. Romans of all classes will be enraged by this. You couldn't do this without honestly centuries of slowly, very slowly, tweaking social and political values to a point where society will accept such a system. In the same way, the USA would collapse probably within a week if you tried to convert it with a single legislative bill to operating in the way that, say, the Duchy/Republic of Milan, or the Hunnic Empire, or even the Roman Republic, was governed.
It is interesting that you say this, because some of the late Roman Emperors were of Germanic Origin, and in the High Middle Ages, there was a German Kingdom that called itself the "Holy Roman Empire", and it had Emperors Otto I, II, and III who sincerely wanted to be Roman Emperors of a newly reconsituted Roman Empire, and they spent alot of their energy trying to conquer the Italian Peninsula so they could legitimately lay claim to being the New Roman Empire. German Emperors eschewing the name of Germany so they could be considered Romans - the very people the original Romans called Barbarians. The Popes were very much against Germans marching into their country, selecting the Pope, and declaring a New Roman Empire, the Italians weren't thrilled at the prospect of Germans trying to rebuild their ancient Roman State, and revisit past Roman Glories. At certain points in their endeavors, these German Emperors almost succeeded, this is almost comical when you think about it, it shows you the attitudes of the Italians and Romans.
Basically what the Romans wanted in the Ancient Period was to
"have their cake and eat it too," they wanted to conquer Europe, yet they were opposed to the dissolusion of their culture, yet their very own imperialism made this inevitable. If the Romans were racist, it was a very limited sort of racism if you ask me. Now what's the average Roman citizen going to do when he settles down on a farm in Germany and he meets this very pretty German barbarian girl, blonde haired blue eyes, about 18 years of age and a very aggreeable German chieftain who encourages his daughter to marry this Roman Citizen whose 30 years old. The Roman citizen shrugs, thinks she's very pretty, and they fact that most of the Italian women are still in Italy, he thinks why not marry the blonde German princess, and so he does, she has many of his children who are half German, those children run around grow up and find more Germans to marry. So what happened to the original Roman Soldiers who settled here and who were thrown into the Gene Pool with all those pretty German women? I think over time, the Germans won, their greatest weapon was pretty German women whom the Roman Soldiers could not resist - they married in, had children with the natives and they disappeared. The Romans conquered a continent and they were so thinly spread and through intermarriage, the natives conquered them. The descendents of those Romans still considered themselves Romans and the late Roman Empire dared not ignore them, but by this time Rome was a Christian Empire with an established hereditary Imperial Monarchy, and all the forms followed by the later medeaval feudal states were already established in this late Roman Empire.
I think the Romans were fairly short-sighted to think they could conquer a whole continent, whose people outnumbered them and think that it would not dillute their culture, it would have been wise of them either not to attempt to build an Empire on this scale with so many subject people, or to take into account that they would be building a new nation with the great influx of people into their Empire. For the Emperors, the more subject peoples, the more income, they built roads all throughout their Empire to tie it together, and they could care less how Roman their subjects were, so long as they paid their taxes. Roman citizens did when citizenship came with the vote, when it didn't they could care less. A suitably inclined Roman Emperor of a later period might have redemocratized the Empire. I think Emperor Constantine for example was concerned for his whole Empire, not just the people of Rome. Constantine was born in what is now Spain at any rate - he could care less what the people of Rome thought and he showed his contempt for them, by moving the Capital to Constantinople in Asia Minor.
So at what point do you think that the Emperors grew so powerful that they could write their own Constitution and total disregard the feeling of the proper Romans in Rome itself? I think that's the key. I think if by chance if someone became Emperor and he was more of "George Washington" type rather than a Nero, he could have wrote his own Constitution and no one would have dared oppose him.
