Technically wake doesn't start till the rotation point.
So for the sake of the discussion we have a 10,000' runway.
MD-11 takes off 18 and rotates at the 6000' marker.
The 737 would have to rotate and be airborne well before the 4000' marker in order to cross paths.
Assuming a no wind condition.
Now the MD11 taking off with a max legal tailwind changes the dynamics but it also changes the rotation point.
The 737 taking off into the headwind would still not encounter the wake.
Try drawing it if that makes any sense.
If we're talking about a 14,000'+ runway and light take off weights you might be able to make it work.
Now a light GA airplane is a completely different story.
And the ATC controller still doesn't make your decisions for you.
If you don't like it you don't go.