Submission would mean them paying you some racketeering monies on a weekly basis. And they would have to give you some cool things for you to either use, or sell. This would force many of the shops in the cities to close down if you're too greedy, as people would become destitute and penniless under your tyrannical rule. Your infamy grows, and now people begin to fear you on sight, having seen your posters everywhere.
About that time, the game would then need to "Radiant Story us up" some new "good guy" heroes to come and try to take you down. A bounty would be issued. Now there's a chance people will recognize you, not as the hero of dragonshout mountain, but as the fallen angel doomed a traitor's death. You would need inside men, inside contact, to trade with, an entire black culture, possibly a dark guild that would harbor such a fugitive as they (along with you) sought power for themselves, trying to vest it from the clutches of the current Empire. Perhaps these ones ally themselves WITH the dragons, and instead of killing dragons to gain shouts, the dragons merely come and tell you the power words directly for the price of a certain kind of rare element you now have to explore to find. This becomes your active main quest now, hunting the rare mineral that fuels the dragons with enormous power beyond their already-formidable talents, meaning now there is no longer anyone to stop them. You lead the dragons to a glorious victory over each city, and as each city falls, it bows to your reign. Armies form to come and dispatch you and your loyal evil followers, and they are tough indeed. But so is your Dragon Army and their fiery death spray. There is just as much quest material in the evil side as there was in the good side, only they're all very different from the quests you saw on the good side. You give tyrannical speeches to terrorize every city to submit without any force needed. If that does not work, you go around, bathing cities that do not bow to you in dragonfire. You raze them to the ground. You determine who is chained and who stays behind to serve you.
But now the main badguy of the game, whoever it is, perhaps some other evil force, also wants to stop you as you are muscling in on his territory and ambitions for the region. That main badguy temporarily forms a truce between himself and good guys in order to take you down. So now you set your sights on taking down the original bad guy as you would have if you played the evil side, so you can try to rule Skyrim totally unopposed. You can, if you are successful, become that tyrant and evil dictator of legend, with every citizen and every evil whim at your disposal. You can rob all their money if you like, and build shrines of you, and force them to worship you. You take the innocent maidens bethrothed to other men and force them to dance for you on the poles, and more. You can beat whomever you like, for sport. You are a dictator god.
OP, are you happy now?