I have completed main and Dawnguard story line, earned all Werewolf perks, finished Civil war and become the leader of all guilds, found 24 fragments of crown, found the priestess of Dibella (recieving active effect, fighting opposite six), forged a crown that makes two standing stones active at the same time, forged Daedric armor for myself, got married. Soon I'm going to become Thane of every Hold, buy a house in every Hold, find every Daedric artifact, find every unique weapon and armor in game, find every Dragon priest mask, make a Dragonbone weapons, find every World Wall, maximize every skill to 100 points, find the skeleton horse in Soul Cairn.
To achieve all this, I will spend several days. But than? Is there anything reasonable to do after this?

Spoilers much?

several "days"?

and no, if you complete all the quests in skyrim, there is nothing more to do for you. you can play skyrim for years, but not with this playstyle.

Either explore the caves and dungeons (worth it a lot of times for some of the unique quests) or start a new character.

On your next round, I'd say take it slow, and explore in between your missions. Dont fast travel. This promotes exploration greatly. And that will prolong the life of your character.

I think TES games aren't suited for your playstyle.

Can you expand your answer please? What is wrong with my playstile?

I don't even understand the question.

You obviously know how the game works, so you should know a few things...
1- You can make a new character with a different type of gameplay.
2- No matter what, one character has not seen or done everything.
3- The game has great replay value.
4- More DLC in the future.

There's also all the Factions to do, which you did not mention.
And these are much more fun to do with low level characters, not some uber level 80 character.
Actually... pretty much everything is funner with a low level character. The game gets boring when there's no challenge and slow progression.

You rush things. Skyrim's like a beautiful lovely classy woman. You gotta take things slow...

Sounds like a pretty messed up character to me.

I dunno... maybe he could collect pots and pans... or perhaps check to see what's in all those barrels he probably breezed by first time... realistically I would actually suggest map-periphery mountaineering: good exercise, nice views, and very occasionally an un-found location.