Sesar is a dream. On the paper.
Let's talk trajectories.
They want to create them as short as possible.
What happens if a plane wants to go from London to Madrid, and an another one (same type, same weight) wants to go from Madrid to London?
Let's make as in some parts of the world : offset track 5 NM right.
Now, let's put another one from Porto to Brussels. And the way back.
The four of them have a meeting over the Atlantic at FL370 on their 4D trajectories calculated by one of the most up to date computers on this planet and... the controler has to deal with the situation.
The ATM computer part of SESAR can't deal with a four traffic conflict (even if the limit was 8).
As an ATCO, I don't want to be the one who will take the situation when the machine screws. My limit is around 8 steady conflicting aircraft (that's an exemple), if the machine's limit is 10 and it screws... then, good luck... "Sorry, unable..."
Your safety could be at stake there.
That's why I don't like it.
And there's also an issue about human factors. (too much assistance so more difficulties to stay focused)
What you are waiting for is the "free route" part of SESAR. On this, I do agree with you.
But it will never be a "free sky for you alone".
And it doesn't solve the airports' capacity problem.