1) The Ottomans could not have made it. One reason was the fact the the Balkans were to hard to control. Another is the fact that there was a lot of infighting between individuals for power and that the Ottoman Empire was so descentralized that it could be easily fractured in two or more entities.

2) The Austro Hungarian Empire is a freak o f history. The fact that it had so many nationalities in its borders means that it could not survive. there's no amount of reform that can make Hungarians and Romanians in Transilvania leave side by side in a an empire neither of them controlled.

3) The Grandgerman Empire would have probably had to germanize the other nationalities between its borders but other than that, with reforms that made the state more centralised and with less political infighting, it probably would have been able to make it to modern times.

4) Napoleaon's Empire... was too damn big, had to many places where it was weak. Couldn't have made it.

5) The Brits could have kept their empire, if it wasn't for their lack of will to do so and for the nation/liberty for the people trend they started. They took away their own empire, really.

6) The Japanese empire had no future because Japan didn't have the power to hold it toghether for long periods of time. It was rather conquered and ocuupid teritory than an empire.

7) Polish Lithuanian Empire. Don't know enough about them, but from what I can gather they had the makings for a great empire. Keeping greater Poland, going into Russia and into ukraine and "polonizing" the people they found their, trying to promote the Catholic faith but allowing for religious freedom, they would have had land and resources. Maybe ading Moldavia and Transilvania and even Valahia would have been possible in time. With reforms and without any major catastrphies, The Polish Lithuanian Empire could have survived. And probably this is the one that deserved too.

What do you think of a Thracian/Dacian Empire, streching from the Black Sea to the North of Italy, pushing into Greece and maybe into southern Poland and Austria?