I finished the main quests and more or less all the side quests (except some Gwen games) and maybe one's I didn't find yet.. also finished all contracts.

I am level 35.

I read that it's capped at level 70. Is it realistic to get somehow remotely close to this?

I don't think you can, probably that cap is set for the expansions to come. But actually a side question here, what's the point? I think the highest armor you can craft is 37 and baddies would stop providing a challenge long before that. Why not just play again.

would be good if they come up with an arena like in the witcher 2 but not outside of the main game,inside the game on an island or something wich you need example required lvl 50 or 70 for ultimate lvl before unlocking kings and mythes
just to have a challenges and not always sleep over to respawn small field mobs.

Or like rift invasion of a zone with somehow like the portal the wild hunt comes in etc...
just like the witches guild does.

And all of a sudden multiplayer login comes on to help eachother with ''arena if it would come"

I'm strongly against anything that encourages grinding or farming. That stuff belongs to the realms of JRPGs, let's leave it there.

Wait for the inevitable game+ dlc

Right now there's no good reason to aim for that level since the game would become extremely boring at this point! Even at level 35 you have to make many mistakes to get killed in battle.

Yes, I agree. I can beat everyone already at 35..

Ok then..

level 70, probably not. Maybe 55-60 after you clear and sell every loot resource in the game. Maybe 65. Maybe.

You need to use the banker who loans you crowns in novigrad. You get 13 xp for every 30 gold you give back to the dwarf banker when you take out a loan and pay it back. That's the only way to do it. At level 35 if you complete every sub-objective on the maps you only hit to about 38. Only way to get higher than that relatively fast is with gold.

I made a macro with my logitech keyboard (logitech gaming software) so I wouldn't have to sit there and manually do this 2000 times. If anyone has a logitech keyboard with gkeys you can do this as well.
The sequence is:
E
E
Space
Space
Space
Space
Enter
Enter
Space
Space
Space
Space
Enter
Enter
Space
Space
Space
Space
E
E
Space
Space
Space
Space
Enter
Enter
Space
Space
Space
Space
Enter
Enter
Space
Space
Space
Space

Set it to Toggle, with 5 Millisecond delay. Make sure "record delays between events" is not on when you input these commands, since you want it to do it as fast as possible with no interruptions.

Just turn it on when you get near the dwarf and then go watch a movie because its going to take at least 2 or 3 hours depending on how much gold you've got to burn. I was level 35 with 72,000. I spent about 50,000 to get to level 46. I could probably make another 50 or 60k if I explore and sell everything that I left on the maps so level 56-58 should definitely be possible if you do this. Anything higher than that though, doubtful unless you grind monsters for gold.

I had no use for in-game money so figured I'd just burn it off by doing this. It seems to be pretty freaking useless. Then again leveling after level 35 seems to be pretty freaking useless as well since you can't do anything with this many skill points. I guess your gear gets way better but other than that doing this in my opinion was pretty useless. The end-game just doesn't really matter at all, like the design of the game just completely falls apart once you hit 35. It IS possible though to hit higher levels, you just need gold to do it though.

I mainly did this because they said they were going to put a cap on gold with the 1.06 hotfix patch. I said F that and decided to burn a lot of gold in the best possible way I knew how before it magically vanished. I recommend anyone with as much as 70k to do the same before 1.06 hotfix hits. You should drop your cash to at least 40k-50k just to be safe. I went further down, to 25k.

Is there a point in leveling after a certain point? You can use a finite number of skills anyway...

What I find strange is I have some diagrams for weapons/armor in the 40's (cant use them yet, I am at level 26). Why have these in the game, even if they are for the expansions??

OK, to see what might happen at "a higher" Level I went to level 70 (by trainer, CHU).

The interesting things to notice: there is gear that can only be used after reaching level 61.
You do not get any exp points from monsters, quests solved will likewise give you not much.

What remains: gear you find, craft, purchase will have ridiculous stats, and at least some monsters/foes are scaling.

Is it any fun to play at this level?
Let me put it this way: if you want to go sightseeing without having to bother a lot about ambushes and such, well - yes it can be still fun to play. How long it will remain to be entertaining - I just can not say, switched back to my normal level in the actual play.

wait for the Next Game + update (rumors are it will be in this week free DLC)
there are already parts of it found by modders in game files

basically only to get stronger gear since gear scales with your level.

But even that is kinda pointless. If you have the best gear at level 35 then yeah, you can pretty much kill anything without a problem at 35.
could be a bug but not sure, I had a diagram for a level 46 steel sword. Like I said its possible to get level 46 legitimately though, you just have to use the dwarf npc who you can ask a loan from and then spend about 50k gold lol.

Here's the easiest method to get there. On a PC open console and type setlevel(70). Done.

maybe some dlc`s bring new content with higher enemies